Freeze the networkstack-aidl-interfaces interface

This freezes the interface as of the latest beta build, not the tip of
tree. IIpClient#setL2KeyAndGroupHint is not in the frozen definition in
particular.

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

Test: flashed, booted, WiFi and captive portal working
Bug: 128803828
Change-Id: Ideabe73fc93bbefca2d624ee9ca190cf31419424