Update Conditions for SignalStrength Unsols

Update and Simplify the signal strength unsol criteria to
better align with other indications. There are two material
changes that result from this:
1) When the device is in Automotive Projection mode or tethering
   is on, signal strength indications will be sent. In both cases
   there is value.
2) Signal Strength indication requests won't fluctuate with the
   device power state when the radio is off.

Bug: 215750179
Test: atest DeviceStateMonitorTest#testAlwaysOnSignalStrengthwithRadioToggle
Change-Id: I8ba4ea97c8847c4060d650cbaf0cd20b28e4ab3d