Don't enable MDNS on non-multicast, non-broadcast interfaces.

This is unlikely to work, and in the case of cell interfaces, it
may be harmful (e.g., use metered bandwidth, or compete for
resources with carrier traffic such as VoLTE).

Bug: 25629907
Bug: 25669326
Change-Id: I2622182ce1a3bb1c605de8afce61cf5ae1f4cbfb
1 file changed