Update internal telephony connection's wifi state.

When the ImsPhoneConnection is updated, pass the state of whether it
is using Wifi to the Telecom Connection. This is done by checking
changes to a Connection's feature capabilities to see if
isVowifiEnabled.

This is a temporary measure. In the long run, this information will
be passed up on the ImsCallSession, and we will need to listen to
WFC handover events.

Bug: 19151548
Change-Id: I53c84cb0169abd72c35407ca3e77952bac30d656