[SCSI] qla4xxx: Implementation of ACB configuration during Loopback for ISP8042

While loopback diagnostic is in progress, disable the ACB which resets
all the active connections to target. Disable ACB would filter out all
the DHCP multicast and broadcast packets which otherwise cause the
diagnostic test to take longer time to complete or failures in some
other cases.

Signed-off-by: Nilesh Javali <nilesh.javali@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>