There were swapped +VGS and +VGM commands which likely caused that speaker volume up key on headset increased microphone gain.

Thanks to leading space in sscanf format, parsing of VGS and VGM commands is whitespace agnostic.

And because pulseaudio does not support other commands then VGS and VGM, it is needed to inform about this fact remote headset by ERROR reply. Also some buggy headsets for ERROR reply send another ERROR command request, so we need to ignore ERROR command.