Alsa: limit buffer size, so shairport can start in time

part1 of the patch series created in my sntp branch but are not necessary to enable the time sync feature

Some USB have a very deep (>2s) buffer.
Having a deep buffer eats up the receiver buffer, so lost packet have less chance of being re-sent in time.
Also, if buffer is 2+s deep, the upcoming time synchronized version will not be able to start in time

increase period size 64 to as big as HW supports: a small period only makes sense for
extremely low latency applications. due to shairport's internal 352 buffer size it makes even less sense