GnssLocationProvider: listening to conn lost event

The HAL layer now gets onLost notificaiton as well
as connectivity available.  This keeps HAL layer
better informed on what the on what the real
connection status is, for things like assistance
download.

Fixes: 34076506
Test: GPS works, even after delete all, and assistance
downloads wait politely when in airplane mode.

Change-Id: I4b5fb782f9370b0a45282c8a9dd5920120d449fb