atmodem: Fix SMS reception for Gemalto modems

SMS reception is not working for Gemalto modems because of +CMT parsing.
PDU length is the first argument of +CMT URCs in Gemalto modems.

Add a switch case on vendor info to handle Gemalto case.
Also handle acknowledgment, +CNMA takes only one parameter.

CMT parsing is moved from at_parse_cmt() to at_cmt_notify(). This
function is modified to match the style of at_cmgr_notify() and it
includes a switch case for CINTERION modems.
1 file changed