qla2xxx: kill sessions/log out initiator on RSCN and port down events

To fix some issues talking to ESX, this patch modifies the qla2xxx driver
so that it never logs into remote ports.  This has the side effect of
getting rid of the "rports" entirely, which means we never log out of
initiators and never tear down sessions when an initiator goes away.

This is mostly OK, except that we can run into trouble if we have
initiator A assigned FC address X:Y:Z by the fabric talking to us, and
then initiator A goes away.  Some time (could be a long time) later,
initiator B comes along and also gets FC address X:Y:Z (which is
available again, because initiator A is gone).  If initiator B starts
talking to us, then we'll still have the session for initiator A, and
since we look up incoming IO based on the FC address X:Y:Z, initiator B
will end up using ACLs for initiator A.

Fix this by:

 1. Handling RSCN events somewhat differently; instead of completely
    skipping the processing of fcports, we look through the list, and if
    an fcport disappears, we tell the target code the tear down the
    session and tell the HBA FW to release the N_Port handle.

 2. Handling "port down" events by flushing all of our sessions.  The
    firmware was already releasing the N_Port handle but we want the
    target code to drop all the sessions too.

Cc: <stable@vger.kernel.org> # v3.18+
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Alexei Potashnik <alexei@purestorage.com>
Acked-by: Quinn Tran <quinn.tran@qlogic.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>