qemu-socket: set passed fd non-blocking in socket_connect()

socket_connect() sets non-blocking on TCP or UNIX domain sockets if a
callback function is passed.  Do the same for file descriptor passing,
otherwise we could unexpectedly be using a blocking file descriptor.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

util/qemu-sockets.c

@@ -910,6 +910,7 @@ int socket_connect(SocketAddress *addr, Error **errp,
     case SOCKET_ADDRESS_KIND_FD:
         fd = monitor_get_fd(cur_mon, addr->fd->str, errp);
         if (callback) {
+            qemu_set_nonblock(fd);
             callback(fd, opaque);
         }
         break;