[SCSI] be2iscsi: Add support for iscsi boot

This patch contains changes for adding support for iscsi_boot.
Have modified to make read of mac address from chip as a function.

  The mac_address is being cached after teh first call as it is
not expected to change

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