NetworkStackClient: Allow modules with network_stack uid

The wifi service will start running with network_stack uid, so allow
modules with the same uid to use the network stack interfaces.

Note: Only modules signed with the same certificate (same as network_stack
APK) can share the uid, so this is restricted to Google signed modules.

Bug: 113174748
Test: Local wifi stack testing
Change-Id: I83263770e5c17dd28e4423e46d82ac8067e98f3a
(Cherry-picked from 51e9edae314f5ef758fff0bf42e12325f8a55362)