Use the wrapped volume interface with the AVRCP conneciton handler

Use the wrapped volume interface in connection handler so that JNI calls
are automatically executed on the correct thread when called from the
connection handler.

Bug: 30602783
Test: Connect a device that doesn't support absolute volume and see that
the JNI call doesn't throw an exception.

Change-Id: Ife768c715022e70dd4055270c1d6cf76ba26aea3