[SCSI] bnx2i : Fix command session number jump issue seen during cable pull test

Without the fix bnx2i would fail tt->xmit_task() when link is down and
libiscsi would have already incremented session->cmdsn before calling bnx2i's
xmit_task() entry point and will just return the command to SCSI-ML when
xmit_task() fails. libiscsi does not retract the session->cmdsn as the command
was never sent on wire.  It is generally good idea for LLD, bnx2i to accept
the scsi cmnd/nopout and let upper layer timeout and go though normal session
recovery process.  When link is down, unsolicited nopout will not be accepted
by bnx2i and connection will never enter recovery state. This fix is required
for MPIO to work corectly

Signed-off-by: Anil Veerabhadrappa <anilgv@broadcom.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>