Remote input: adjust buffer sizes to sample rate

Remote input: adjust buffer sizes to sample rate

Covers both the sample sink FIFO and the receiving buffer size from UDP stream. The latter is sized in number of complete FEC protected frames of about 64 kB. Minimum is 4 frames and otherwise adjusted to fit about 2 seconds independently of the sample rate. Thus for rates above ~48 kS/s the delay will be constant at approximately 2 seconds. For higher sample rates this should facilitate buffer synchronization for a smoother stream at the expense of a slightly longer delay. The sample sink FIFO size is also adjusted which should also facilitate smooth operation. Hopefully this will improve working at higher sample rates while reducing the delay at lower sample rates.

Implements #534