Take the multicast lock on mDNS usage

When an mDNS request (discovery, advertising, resolving...) is
registered and gets assigned a socket on a wifi network, take the
multicast lock to ensure that it can reliably receive mDNS responses.

This is limited to when the application has importance
FOREGROUND_SERVICE or higher.
NsdManager is not documented to require usage of the multicast lock,
which has caused various reports about its reliability. Taking the lock
while the app is in the foreground should address the large majority of
cases, while limiting battery impact.

Going forward this should allow developers on U+ to not take the
lock themselves, allowing optimizations on devices supporting APF,
where instead of taking the lock APF would let through only select
mDNS packets.

Bug: 284389438
Test: atest
Change-Id: I1ce85220eac4a1529b6716d50727c1c462356846