Guard against creating too many MobileSignalControllers

The PhoneStateListener that got added to NetworkControllerImpl used the
default (main) looper for its callbacks, which caused race conditions
when updating subscriptions. This resulted in zombie
MobileSignalControllers that were untracked and never stopped listening
for their updates.

To fix the problem we put the phone state listener on the same
background thread as the receiver handler, and also lock around updating
the subscriptions so that we can all have peace of mind.

This should fix a host of issues where the mobile signal is incorrectly
showing state such as disconnected or not showing the data type
indicator.

Fixes: 129717207
Test: visual; remove and insert sim and verify that the proper SIM state
is shown

Change-Id: Iace6a04c0629e24d2ef9c980a8de336a225d0f36