Close fd's of persistent tap devices

When passing a NULL tapfd argument to brAddTap, we need to close the fd
of the tap device. If we don't, libvirt will keep the fd open
indefinitely and renders the the guest unable to configure its side of
the tap device.
Signed-off-by: NSoren Hansen <soren@linux2go.dk>

src/util/bridge.c

@@ -538,6 +538,8 @@ brAddTap(brControl *ctl,
         goto error;
     if (tapfd)
         *tapfd = fd;
+    else
+        close(fd);
     return 0;
 
  error: