Freeze networkstack-aidl-interfaces as version 3.

IIpClient#addNattKeepalivePacketFilter is the only difference
between version 2 and 3.

Generated with: m networkstack-aidl-interfaces-freeze-api

Test: -builds, boots
      - atest NetworkStackTests
      - atest ConnectivityServiceTest
Bug: 128803828

Change-Id: I22333c3c5930415cc43d83bc8cc6f566d0acb1f2
(cherry picked from commit 36bf793ce0a113a99252c2a640338bcf99965319)