be2iscsi: Fix ExpStatSn in management tasks

Connection resets observed from some targets when NOP-Out with wrong
ExpStatSn is sent.

FW keeps track of StatSn and fills up ExpStatSn accordingly.  The header
filled up by the stack needs to be modified by driver to clear
ExpStatSn. If the field is not cleared, FW recalculates ExpStatSn and
wrong offset'ed ExpStatSn is seen in the wire trace.

Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>