net/udp: fix conn_unlock not called outside conditional block

Move conn_unlock() call outside the if block in psock_udp_sendto()
to ensure the connection lock is always released before returning,
preventing a potential deadlock when the condition is not met.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

net/udp/udp_sendto_buffered.c

@@ -895,10 +895,10 @@ ssize_t psock_udp_sendto(FAR struct socket *psock, FAR const void *buf,
           conn_unlock(&conn->sconn);
           goto errout_with_wrb;
         }
-
-      conn_unlock(&conn->sconn);
     }
 
+  conn_unlock(&conn->sconn);
+
   /* Return the number of bytes that will be sent */
 
   return len;