[SCSI] libfc: in fc_lport_destroy, flush rports after turning off link

During an fcoe module unload, we saw a problem where fc_rport_work()
finds the lport has been freed.  The rdata points to an area
containing 0x6b6b6b6b... the pool poison value from kmem_free().

In fcoe_if_destroy() we call fc_fabric_logoff() then fc_lport_destroy().
fc_fabric_logoff() flushes the remote port work, but we're still receiving
requests, and an RSCN or PLOGI arrives which creates more rports.

Note that although the LLD also checks link_up, it doesn't do it
under the lport mutex, so it can deliver frames to
fc_lport_recv_req() even after link_up is cleared.
So, re-check link_up there.

We need to flush the rports by calling disc_stop_final()
after we clear link_up.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>