vlc: fix bonjour support

bonjour support checks for avahi-client, which requires avahi-daemon and
dbus enabled.

Fixes:
  http://autobuild.buildroot.org/results/f8b/f8bed9a42f1853db8aa81161d7be5a7cb67afe8f/build-end.log



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>