Make the wait in cfiscsi_offline() interruptible. This is the second half
of the fix/workaround for the "ctld hanging on reload" problem.

PR: 220175
Reported by: Eugene M. Zheganin <emz at norma.perm.ru>
Tested by: Eugene M. Zheganin <emz at norma.perm.ru>
Approved by: re (kib)
MFC after: 2 weeks
Sponsored by: playkey.net