unit: move all data_call tests to test-grilunsol.c

Fixed unit tests due to merge of grilreply data_call
parsing code into the grilunsol version that handled
data_call_list change events.  Also re-worked data/voice
registration tests to check RADIO_TECH values as opposed
to the high-level ofono constants.
rilmodem: modify gprs-context event logic

This change makes an instance of gprs-context
only listen for data_call_list messages when
it's primary context has been activated.  It
also adds details to the DBG messages to help
differentiate the different context instances.