AVRCP volume reporting for A2DP profile
I couldn't find any already exisiting ticket for that, so creating one. Citing @tanuk from #361 (comment 13954):
If the user changes the headset volume in the A2DP mode, PulseAudio doesn't know that the headset volume changed. With A2DP there are two volume controls that affect the final volume: the volume that PulseAudio applies, and the volume that the headset applies. This is bad user experience, but at least in the past bluetooth simply didn't provide a way to sync the two volumes. I think newer bluetooth versions have added the necessary functionality, but it hasn't been implemented in PulseAudio.
With Wireshark, I can see AVRCP volume events being sent while pressing volume buttons on the devices, so I guess that's the profile that needs to be supported there.