MFC r314086: Fix multiple problems around LUN disable under load.

MFC r314086: Fix multiple problems around LUN disable under load.

 - Move private data about ATIOs/INOTs from per-LUN to per-channel data.
This allows active commands to continue operation after LUN destruction.
This also simplifies lookup of the data by tag in some situations.
 - Unify three restart_queue processing implementations.
 - Complete all ATIOs from restart_queue on LUN disable.
 - Delete ATIO private data when command completed or aborted, not depending
on the ATIO being requeued, that was ugly hack and could never happen.  CAM
should always call ether XPT_CONT_TARGET_IO with status or XPT_ABORT.
 - Implement XPT_ABORT for queued ATIOs/INOTs to allow CAM do graceful
shutdown, not depending on LUN disable, as it is done in ahd(4)/targ(4).
 - Unify isp_endcmd() arguments to make it more usable in generic code.
 - Remove never really used LUN state reference counter.

git-svn-id: svn://svn.freebsd.org/base/stable/10@314733 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f