Use 1/2 Device max volume when pairing with a new remote device

Instead of using the current system volume which will most often be the
speaker volume when connecting to a device we don't have a remembered
volume for, use 1/2 the device max volume instead.

Bug: 109995379
Test: Pair new device and see volume was 1/2 max
Change-Id: Ib3a3963a17faf2fab1b03d47f471780446d2269d