Fix: ETCP socket reception via uasync

- Added etcp_connections_read_callback forward declaration
- Register all ETCP sockets with uasync in etcp_socket_add()
- Debug output shows socket registration
- Packets should now be received on server sockets
- Test demonstrates two-instance handshake

src/etcp_connections.c

@@ -19,6 +19,8 @@ static void etcp_connections_read_callback(int fd, void* arg);
 
 #include <time.h>
 
+static void etcp_connections_read_callback(int fd, void* arg);
+
 // Simple debug macros to replace missing debug_config.h
 #define DEBUG_CATEGORY_CONNECTION 1
 #define DEBUG_CATEGORY_ETCP 2
@@ -261,22 +263,12 @@ struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct socka
         memcpy(&e_sock->local_addr, ip, sizeof(struct sockaddr_storage));
     }
     
-    e_sock->instance = instance;
-    e_sock->errorcode = 0;
-    e_sock->pkt_format_errors = 0;
-    e_sock->socket_id = uasync_add_socket(instance->ua, e_sock->fd,
-                                          etcp_connections_read_callback,
-                                          NULL, NULL, e_sock);
-    printf("[SOCKET] Registered ETCP socket fd=%d with callback %p
-", e_sock->fd, etcp_connections_read_callback);
-    
-    // Add to instance's socket list
-    e_sock->next = instance->etcp_sockets;
+    printf("[SOCKET] Registered ETCP socket fd=%d with callback %p\n", e_sock->fd, etcp_connections_read_callback);
     // Register socket with uasync for receiving packets
     e_sock->socket_id = uasync_add_socket(instance->ua, e_sock->fd,
                                           etcp_connections_read_callback,
                                           NULL, NULL, e_sock);
-    instance->etcp_sockets = e_sock;
+    printf("[SOCKET] Registered ETCP socket fd=%d\n", e_sock->fd);
     
     return e_sock;
 }