AESinkPULSE: Try to use default alternate-samplerate 48000

PA has an alternate sample concept, which allows a sink that is normally running with 44.1 khz to switch to 48 khz.

In order to easy upsample / downsample we use 48000 whenever it makes sense.

Best case: Audio gets to the sink without resampling in 48 khz and in 44.1 khz

Worst case: someone resamples actively to 48 khz and that will be resample later by pulse, cause it is not using the device exclusively and cannot resample therefore.