Fix mesh topology handling with fallback to normal decryption

When receiving packets on client links, try INIT decryption first.
If it fails (e.g., for INIT_RESPONSE packets), fallback to normal
decryption using the existing link's crypto context.

This fixes mesh topology where both nodes send INIT simultaneously,
while maintaining compatibility with standard client-server mode where
client links receive INIT_RESPONSE packets.

Changes:
- If link==NULL OR link is client (is_server==0), try INIT decryption
- On any INIT decryption error, if we have an existing link, goto normal_decrypt
- Added normal_decrypt label before standard packet processing
- This allows handling both incoming INIT (create server link) and
  incoming responses (use existing client link) correctly

src/etcp_connections.c

@@ -577,7 +577,16 @@ static void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
     if (link==NULL || link->is_server==0) {// пробуем расшифровать, возможно это init
 //        printf("[ETCP DEBUG] No existing link found, trying to decrypt as INIT packet\n");
         struct secure_channel sc;
-        if (recv_len<=SC_PUBKEY_SIZE) { errorcode=1; DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "etcp_connections_read_callback: packet too small for init, size=%zd", recv_len); goto ec_fr; }
+        if (recv_len<=SC_PUBKEY_SIZE) {
+            DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "etcp_connections_read_callback: packet too small for init, size=%zd", recv_len);
+            // If we have an existing link (client link), try normal decryption instead
+            if (link != NULL) {
+                DEBUG_INFO(DEBUG_CATEGORY_ETCP, "INIT packet too small, trying normal decryption with existing link");
+                goto normal_decrypt;
+            }
+            errorcode=1;
+            goto ec_fr;
+        }
         sc_init_ctx(&sc, &e_sock->instance->my_keys);
 //        printf("[ETCP DEBUG] Extracting peer public key from position %ld, total packet size=%zd\n", recv_len-SC_PUBKEY_SIZE, recv_len);
 //        printf("[ETCP DEBUG] Last 64 bytes of packet (PUBKEY): ");
@@ -588,11 +597,21 @@ static void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
         
         if (sc_set_peer_public_key(&sc, &data[recv_len-SC_PUBKEY_SIZE], SC_PEER_PUBKEY_BIN)!=SC_OK) { 
             DEBUG_ERROR(DEBUG_CATEGORY_CRYPTO, "etcp_connections_read_callback: failed to set peer public key during init");
+            // If we have an existing link (client link), try normal decryption instead
+            if (link != NULL) {
+                DEBUG_INFO(DEBUG_CATEGORY_ETCP, "INIT peer key setup failed, trying normal decryption with existing link");
+                goto normal_decrypt;
+            }
             errorcode=2; 
             goto ec_fr; 
         }
         if (sc_decrypt(&sc, data, recv_len-SC_PUBKEY_SIZE, (uint8_t*)&pkt->timestamp, &pkt_len)) {
             DEBUG_ERROR(DEBUG_CATEGORY_CRYPTO, "etcp_connections_read_callback: failed to decrypt init packet");
+            // If we have an existing link (client link), try normal decryption instead
+            if (link != NULL) {
+                DEBUG_INFO(DEBUG_CATEGORY_ETCP, "INIT decryption failed, trying normal decryption with existing link");
+                goto normal_decrypt;
+            }
             errorcode=3; 
             goto ec_fr; 
         }
@@ -609,7 +628,16 @@ static void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
            } *ack_hdr=(void*)&pkt->data[0];
         uint64_t peer_id;
         memcpy(&peer_id, &ack_hdr->id[0], 8);
-        if (ack_hdr->code!=ETCP_INIT_REQUEST && ack_hdr->code!=ETCP_CHANNEL_INIT) { errorcode=4; DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "etcp_connections_read_callback: not an init packet, code=%02x", ack_hdr->code); goto ec_fr; }// не init
+        if (ack_hdr->code!=ETCP_INIT_REQUEST && ack_hdr->code!=ETCP_CHANNEL_INIT) {
+            DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "etcp_connections_read_callback: not an init packet, code=%02x", ack_hdr->code);
+            // If we have an existing link (client link), try normal decryption instead
+            if (link != NULL) {
+                DEBUG_INFO(DEBUG_CATEGORY_ETCP, "Packet is not INIT (code=%02x), trying normal decryption with existing link", ack_hdr->code);
+                goto normal_decrypt;
+            }
+            errorcode=4;
+            goto ec_fr;
+        }// не init
 
         struct ETCP_CONN* conn=e_sock->instance->connections;
         while (conn) {// ищем есть ли подключение к этому пиру
@@ -688,6 +716,7 @@ static void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
         return;
         }
 
+normal_decrypt:
     DEBUG_INFO(DEBUG_CATEGORY_ETCP, "Decrypt start");
     if (sc_decrypt(&link->etcp->crypto_ctx, data, recv_len, (uint8_t*)&pkt->timestamp, &pkt_len)) { 
         DEBUG_ERROR(DEBUG_CATEGORY_CRYPTO, "etcp_connections_read_callback: failed to decrypt packet from node %llu len=%d", (unsigned long long)link->etcp->instance->node_id, recv_len);