In the case a unsolicited indication for UREG was received
while the status was polled. The poll response failed to parse.
This since the unsolicited indication only carries one
parameter, while the poll response is expected to carry two.
Update the code to loop until the response is found.
The log below shows a case where this happened.
10:07:55 ofonod[520]: Aux: > AT+UREG?\r
10:07:55 ofonod[520]: Aux: < \r\n+CGREG: 4\r\n\r\n+UREG: 0\r\n\r\n+CIEV: 9,1\r\n
10:07:55 ofonod[520]: src/gprs.c:ofono_gprs_status_notify() /ublox_0 status unknown (4)
10:07:55 ofonod[520]: src/gprs.c:ofono_gprs_detached_notify() /ublox_0
10:07:55 ofonod[520]: Aux: < \r\n+UREG: 1,0\r\n
10:07:55 ofonod[520]: Aux: < \r\nOK\r\n
It turns out that both L2xx and L4xx modems are a bit
buggy when it comes to send CREG URC's when the tech changes.
Try to overcome this by subscribing to both UREG and CREG,
and poll the other when any of the URC's are received.
Protect from doing simultaneous polls though.
For uBlox modems, a bit of custom setup is required, but after that the
generic "atmodem" (27.007-compatible) method implementations are
sufficient. This driver, therefore, just puts the custom probe method
into place and defers remaining functionality to the recently exported
atmodem implementations.