Fixed roaming related issues

1. the data enable check will be performed in trySetupData so
there is no need to add additional check in onRoamingOff and
onRoamingOn.

2. Do not trigger set initial attach apn and set data profile
in onRoamingOn (revert this behavior back to N-MR2).

3. Renamed getDataOnRoamingEnabled to getDataRoamingEnabled
for consistency.

bug: 30936226, 37280015
Test: Telephony sanity tests

Merged-In: I30ce763468b3068ecd80ab2a6a313b6284016909
Change-Id: I30ce763468b3068ecd80ab2a6a313b6284016909