Fix call disconnect issue in LTE->1x CSFB.

When registered in LTE, phone object is switched to GSM.
Attempting a CSFB MO call will cause the phone object to be
switched to CDMA resulting in local hangup of the dialled call.
To fix this, do not switch phone object to GSM when camped to LTE
in CDMA-LTE mode.
If there is a real need to switch to GSM it is done via
RIL_UNSOL_VOICE_RADIO_TECH_CHANGED.

Change-Id: Ibbde3d284fa823cc74e41697b5ef41ead6c33093
CRs-Fixed: 578578