[rilmodem] Checking if phone is really roaming

In case of virtual operators it looks like it is possible that
modem is indicating roaming state even though that is not true.
With this fix status is double checked against EF SPDI.

Signed-off-by: Jussi Kangas <jussi.kangas@oss.tieto.com>
Merge pull request #90 from jkangas/master

Request for pulling checking the network status based on SPDI check in rilmodem to main branch