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

[Nachtzuster]

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