qla2xxx: disable scsi_transport_fc registration in target mode

There are multiple reasons for disabling this:

1. It provides no functional benefit. We pretty much only get a few more
sysfs entries for each port, but all that information is already
available from /sys/kernel/debug/target/qla-session-X

2. It already only works in private-loop mode. By disabling we'll be
getting more uniform behavior with fabric mode.

3. It creates complications for the new PLOGI handling mechanism:
scsi_transport_fc port deletion timer could race with new session
from initiator and cause logout after successful login.

Cc: <stable@vger.kernel.org> # v3.18+
Signed-off-by: Alexei Potashnik <alexei@purestorage.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>