Extend the maximum number of allowed PCM channels in a PCM stream to
127 and decrease the maximum number of sub-channels to 1. These
definitions are only used inside the kernel and can be changed later
if more than one sub-channel is desired. This has been done to allow
so-called USB audio rack modules to work with FreeBSD.

Bump the FreeBSD version to force recompiling all external modules.

MFC after: 2 weeks
Reviewed by: mav