[iwlan] clean up data connections on service restart

Not all vendor implementations of Iwlan data service can support
persistence of iwlan tunnels across service crash/restart

Use case impacted:
1) Make IMS wifi call
2) kill iwlandataservice
3) Next call/registration on iwlan fails.

This change introduces a new config based on which
telephony framework can take action to clean up dangling
data connections in case iwlan service restarts

Bug: 158043105
Tests: on device test involving killing/restart of data service.
       verifying subsequent wifi calls work.
Change-Id: Ifd95ff4d11a61b8a8e199c916bf57eeb04144868