sound: Honor CHN_F_NBIO

If the device is opened with O_NONBLOCK, even though we check for it in
order to set CHN_F_NBIO, the subsequent chn_reset() calls will clear all
flags, except those set in CHN_F_RESET, which does not include
CHN_F_NBIO.

Add CHN_F_NBIO to CHN_F_RESET. Additionally, because primary channels
can be reused, make sure we do not unintentionally keep CHN_F_NBIO set
if the channel is re-opened, but without O_NONBLOCK.

PR: 289441
MFC after: 2 days
Reviewed by: christos, markj
Differential Revision: https://reviews.freebsd.org/D52493