SubscriptionController: Default to DDS flexmap triggering

This changes the default so that the AOSP behavior prevails over
qualcomm-specific implementations that use telephony-fwk.

This change explicitly triggers a request to update modem capabilities
when the data sub is changed thus allowing the second subscription
to go over 2G, which wasn't possible previously.

Change-Id: I20dd586ea74af7ba8ef6a1ce1cdd26c07d33d844