When in trunking mode, the adapter can be placed into diagnostic mode and
each link in the trunk tested via loopback.

Add support to the driver to perform per-link loopback testing when in
trunking mode.
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>