Send last discovery preference to provider service

To ensure discovery preference is delivered to the provider service,
it delivers the discovery preference whenever the connection is
established.
Without this CL, discovery preference may not be delivered to the
service when rebindIfDisconnected is called in the middle of connecting.

Bug: 151128724
Test: cts test and atest mediaroutertest
Change-Id: I723298f108a0a7d3217c997be362e43764313bae