Allow network stack UID caller to retrieve cell identity

For backwards compatibility, we allow phone, system UID to
access cell identity through getServiceState. Cell broadcast
service, which is used to be part of telephony, now is running
under network stack UID. We should consider network stack UID as
trustable components like system/telephony.

Fix: 157618105
Test: Manual
Change-Id: I9b2dfc778752e130f5c7e44c4b2e45b63ac6f918