BSC_ConnectionHandler.ttcn: split up f_mt_sms() into two functions

This would allow to expect a MT SMS message using f_mt_sms_expect()
and send an RP-ACK using f_mt_sms_send_rp_ack() separately in the
follow-up changes for SMS over GSUP.

Change-Id: I4730634a9f3352b6f8553ee2fd1d43044f41241e
1 file changed