Reduce race between LUN destruction and request arrival.

MFC after:	1 week
Remove bunch of unused lun variables.

MFC after:	1 week
Add missing error checking for kernel_port_{add,remove}().  Both can fail
for reasons yet unknown; don't make it increment cumulated_error as a kind
of temporary workaround.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Simply remove the tmp dir before creating the symlink. We are doing
chroots all over the place, so there is bound to be a stale file lying
around in there (in my case samba lock files from creating accounts). If
we don't do that, the symlink later will fail.
Close race between cfiscsi_offline() and new connection arrival.

Incoming connection should be either rejected or accepted and terminated.
Document use of wildcards (*) and ampersands (&) in autofs map files.

Differential Revision:	https://reviews.freebsd.org/D1199
Reviewed by:	wblock@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Fix error handling.

MFC after:	1 month
Coverity CID:	1249768
Sponsored by:	The FreeBSD Foundation
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/userlandenhanced