gril: Fix parsing of registration state replies

There were two bugs when parsing voice/data registration state replies:
the status value could be one not recognized by ofono and the max number
of call ids was not being set properly for MTK modems. This commit fixes
both issues.
unit: Add tests for more rild status codes
Merge pull request #120 from alfonsosanchezbeato/fix-empty-status

gril: Fix parsing of registration state replies