Fix compilation issues

Library dl is missing and it prevents compilation in some platforms.
Remove unused variables, convert signed to unsigned when required.
Change gprs initialization order

Previously GPRS initialization was done after modem has been powered up but
before it is set online. One RIL implementation returns error because
it cannot initiate the GPRS initialization while offline. Moved the GPRS
initialization to be done after modem is set online.
Accept IPV4 as IP

New RIL reports IPV4 instead of IP. Accept it as IP.
Run ofono as radio user

Sandbox ofono into radio user to be compatible with ril.