Add version-based visibility of shairport-sync endpoints

Add version-based visibility of shairport-sync endpoints

This patch introduces modification to AirPlay attributes allowing AirPlay clients
seeing only appropriate Endpoints of specific version of AirPlay protocol.

[Test]
Run two instances of shairport-sync - built for version 1 and for version 2.

TuneBlade recognizes only AirPlay version 1 instance running.
MacOS/iOS recognizes only AirPlay version 2 instance running.

Without that patch, both MacOS/iOS detect two endpoints at the same time.
The TuneBlade detects only AirPlay version 1 since it doesn't support AirPlay version 2.