ConnectivityService: Grant networkstack uid extra privileges

The wifi network factories/agents are going to run in the network stack
process for devices which accept wifi mainline module. Allow these
factories/agents to perform privileged operations.

Bug: 142115344
Test: ACTS test
Change-Id: I2dd412ac5c6b67f52c87113fcda345e1f531f9c4
WifiNetworkRequestTest:test_connect_failure_user_rejected passes now.
(cherry-picked from c7580b1d59ee126cd6867cb6fe4485a69e2b4622)