Code review comment for lp:~awe/phablet-extras/ofono-gprs-support

I just re-factored the DATA_CALL response code based on feedback from cyphermox:

1. The code that calculates netmasks has been moved to rilutil, so that it can be unit-tested ( TODO ).

2. The code now handles multiple IP address and/or gateways returned from RILD in a more graceful manner, in that it splits the addresses, and only hands the first address and gateway to the core ofono code ( which only handles single IP addresses and gateways ).

3. The code now strips IP address prefixes, as NM doesn't handle them properly.