sip: get local TCP address in establish handler (#146)

After calling tcp_connect(), the address returned by
tcp_conn_local_get() is 0.0.0.0 on some platforms (Windows).

The local address of the TCP-connection is not available
until the TCP connection is fully established, so fetch the
address again in the established handler.

Reference: https://github.com/alfredh/baresip/issues/431

src/sip/transp.c

@@ -459,6 +459,10 @@ static void tcp_estab_handler(void *arg)
 	struct le *le;
 	int err;
 
+#ifdef WIN32
+	tcp_conn_local_get(conn->tc, &conn->laddr);
+#endif
+
 	conn->established = true;
 
 	le = list_head(&conn->ql);