audio/pulseaudio-module-xrdp: improve audio redirection latency

by backporting from upstream. PulseAudio >= 12 become more strict.
This patch reduces network bandwidth and CPU usage of xrdp.

While here, set DIST_SUBDIR=xrdp for xrdp related ports.

Obtained from: https://github.com/neutrinolabs/pulseaudio-module-xrdp/pull/38