scsi: lpfc: Inhibit aborts if external loopback plug is inserted

In the Linux kernel, the following vulnerability has been resolved:

scsi: lpfc: Inhibit aborts if external loopback plug is inserted

After running a short external loopback test, when the external loopback is
removed and a normal cable inserted that is directly connected to a target
device, the system oops in the llpfc_set_rrq_active() routine.

When the loopback was inserted an FLOGI was transmit. As we're looped back,
we receive the FLOGI request. The FLOGI is ABTS'd as we recognize the same
wppn thus understand it's a loopback. However, as the ABTS sends address
information the port is not set to (fffffe), the ABTS is dropped on the
wire. A short 1 frame loopback test is run and completes before the ABTS
times out. The looback is unplugged and the new cable plugged in, and the
an FLOGI to the new device occurs and completes. Due to a mixup in ref
counting the completion of the new FLOGI releases the fabric ndlp. Then the
original ABTS completes and references the released ndlp generating the
oops.

Correct by no-op'ing the ABTS when in loopback mode (it will be dropped
anyway). Added a flag to track the mode to recognize when it should be
no-op'd.