Route GPS notifications to all users.

This takes the easy way around notifying the correct users
about GPS state transitions by notifying ALL the users(!).

I've also laid groundwork for proper multiuser support in
LocationManager and did a tiny bit of cleanup in
GpsNetInitiatedHandler while I was looking at notifications.

Bug: 7213552
Change-Id: I2d6dc65c459e55d110ac0f5f79ae7a87ad638ede