Implement onServiceConflict

Implement the onServiceConflict callback in MdnsAdvertiser, refactoring
the conflict detection to reuse it both in onServiceConflict (when a
conflict is detected on the network after add) and at service add time.

Bug: 241738458
Test: atest MdnsAdvertiserTest
Change-Id: I69128db936296bd2c5e90e9f00df19fd881e1748
2 files changed