package/mpd: enable neighbor discovery support

Enable support for neighbor discovery useful in Samba and UPnP networks.

[Thomas: add dependency on smbclient or upnp plugin, without which the
neighbor discovery support isn't very useful.]

Signed-off-by: Jörg Krause <jkrause@posteo.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>