CTL: Fix double command completions on HA failover.

I've found couple cases when CTL_FLAG_SENT_2OTHER_SC flags were not
cleared on commands return from active node or the send failure. It
created races when ctl_failover_lun() call before ctl_process_done()
could cause second ctl_done() and ctl_process_done() calls, causing
all sorts of problems.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.