MFC r331013:
Fix iSCSI target crash on session reinstation.
The crash scenario goes like this: there's a thread waiting on "reinstate";
because it doesn't update the timeout counter it gets terminated by the
callout; at this point the maintenance thread starts the termination routine.
The first thread finishes waiting, proceeds to icl_conn_handoff(), and drops
the refcount, which allows the maintenance thread to free its resources. At
this point another thread receives a PDU. Boom.
PR: 222898, 219866
Sponsored by: playkey.net