Centralize IP neighbor monitoring in BpfCoordinator

This CL centralizes IP neighbor monitoring in the BpfCoordinator,
eliminating the need for redundant monitors in each IpServer.

Test: atest TetheringTests
Bug: 294025403
Change-Id: Ie6fbc3eeaa0ed4a34a6680714f44678e2d5b633a
4 files changed