drivers/unix_socket: Ignore additional clients

Only one client connection is supported now, so ignore new ones as long as the
current connection is not severed.

Author: Lluís Vilanova

core/drivers/unix_socket.cc

@@ -80,6 +80,9 @@ void UnixSocketPort::AcceptThread() {
       }
       if (fd < 0) {
         PLOG(ERROR) << "[UnixSocketPort]:accept4()";
+      } else if (client_fd_ != kNotConnectedFd) {
+        LOG(WARNING) << "[UnixSocketPort]: Ignoring additional client\n";
+        close(fd);
       } else {
         client_fd_ = fd;
       }