IP connectivity metrics: update ipconnectivity.proto

This patch adds several new fields to ipconnectivity.proto for
improving APF metrics, connect metrics, and link_layer inference.

Test: build, flashed, ran $ adb shell dumpsys connmetrics list proto
      updated metrics unit tests depending on proto schema
Bug: 34901696
Change-Id: I6f68e16f583a6b407f33f8a500133e100f3453c7