[SCSI] be2iscsi: Limit max_xmit_length

This patch limits max_xmit_length to 64K incase older
utilities are used

Signed-off-by: Jayamohan Kallickal <jayamohank@serverengines.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>