Framework: Fix GSM signal strength

Certain OEM gsm ril libs send back a bogus value for LTE signal
that causes SignalStrength.java to default to LTE and report
incorrect signal values.
Use prop value ro.telephony.ril.v3=signalstrength to get proper
GSM signal reading on certain devices.

Change-Id: Ibb23d7b3a2d21001ccbbc6ebfbdc3c5248f18cfc
Signed-off-by: dhacker29 <davidhackerdvm@gmail.com>