telephony: SignalStrengh: Don't calculate a LTE snr if the srq is invalid

If the previous values are invalid and signal quality is -1, chances are there's
no LTE signal at all, so don't calculate the SNR and mark it invalid as well.

This fixes the strength indicator in GSM devices where it was being skewed
by the ghost LTE value

Change-Id: I070573401c141aa99941a332ee256246697abb90
core and telephony: Additional HSPAP support

Change-Id: I5e921d2308d873678d6ef67a91cff50d383a176b
TelephonyManager: isSmsCapable: respect telephony properties

The 2 telephony properties override if SMS send/receive is enabled
in the telephony code. Also respect them for the isSmsCapable API.

Use case: Acer A700/701 (Wi-Fi only/3G) share the same build

Change-Id: Iaa1b45c62fa5a48a4c4a222d5e47980dd1678d48