Check system_server PID in NetworkStack calls

Add a check that callers with UID 1000 always have the same PID. This is
a proxy for checking that no system is designed to bind to the network
stack unless it is the system_server, as otherwise either the
system_server would start crashing, or that system would not have access
to binder calls.

Also remove access from PHONE_UID as it is not being used.

Test: Flashed, WiFi working, Bluetooth reverse tethering shows no
      permission issue.
Bug: 133209255
(patched automatically from Ib848aaaedfd599c1d4437378846c7dda74352019)
(command: git -C [qt repo] show -p 4895c5 | patch -p3)

Merged-In: I1205ae4b1062fe78f1e2283d6c308caa58651e86
Change-Id: I42215bd8b14d66d0150e7dac04fbb28feef991a6