ALSA reports monotonic timestamps regardles of the time stamps type set
by snd_pcm_params_set_tstamp_type(). Calculate delta between FPGA time
and ALSA time when audio stream starts and use this delta to correct
time stamps in SR packets.

Second mmap to the fixed address in the end of the first mmapped buffer
results in application crash. Do not use double mmapping and process
buffer roll over.