Log NUD failure metrics upon neighbor losts due to MAC address changes.

When the probed neighbor is default gateway, checking if the MAC address
has changed is required. If MAC address does change, log the NUD metrics
while triggering the neighbor lost callback.

Bug: 162944199
Test: atest NetworkStackTests
Change-Id: I8315b11b75c83be2a58c9891589f2e582083bbda