Remake Linux' SOUND_MIXER_INFO IOCTL as a wrapper around new FreeBSD's one.

Submitted by:	Dmitry Luhtionov <dmitryluhtionov@gmail.com>
MFC after:	3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272059 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f