debug: add ERROR-level logs for INIT padding calc (req+resp)

Shows mtu, s_rand, s_max, offset/xoffset, and whether capped.
RESP: removed old hardcoded 1472+26 cap, replaced by formula.
Both paths use consistent formula based on #defines.

src/etcp_connections.c

@@ -134,7 +134,8 @@ static void etcp_link_send_init(struct ETCP_LINK* link, uint8_t reset) {
     // padding
     int s = rand() % (link->handshake_maxsize - link->handshake_minsize) + link->handshake_minsize;
     int s_max = (int)(link->mtu) - 3 - (int)SC_TAG_SIZE + (int)UDP_SC_HDR_SIZE - (int)SC_PUBKEY_ENC_SIZE;
-    if (s > s_max) s = s_max;
+    DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "INIT_REQ: mtu=%d s=%d s_max=%d offset=%zu", (int)link->mtu, s, s_max, offset);
+    if (s > s_max) { DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "INIT_REQ capped s=%d -> %d", s, s_max); s = s_max; }
     if (s < 0) s = 0;
 
     int to_add=s-offset-UDP_HDR_SIZE - UDP_SC_HDR_SIZE;
@@ -1531,9 +1532,12 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
     int xoffset=sizeof(*ack_repl_hdr);
     // padding
     int s = rand() % (link->handshake_maxsize - link->handshake_minsize) + link->handshake_minsize;
-    if (s > link->mtu) s = link->mtu;
-    // Cap s: final encrypted = s - 26 for RESPONSE (noencrypt=0)
-    if (s > 1472 + 26) s = 1472 + 26;  // s ≤ 1498
+    int s_max = (int)(link->mtu) - 3 - (int)SC_TAG_SIZE + (int)UDP_SC_HDR_SIZE;
+    DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "INIT_RESP: mtu=%d s=%d s_max=%d xoffset=%d", (int)link->mtu, s, s_max, xoffset);
+    if (s > s_max) { DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "INIT_RESP capped s=%d -> %d", s, s_max); s = s_max; }
+    if (s < 0) s = 0;
+    // Remove old hardcoded caps
+    // if (s > 1472 + 26) s = 1472 + 26;
 
     int to_add=s - xoffset - UDP_HDR_SIZE - UDP_SC_HDR_SIZE;
     if (to_add<0) to_add=0;