[SCSI] libfc: re-login to remote ports that send us LOGO

[SCSI] libfc: re-login to remote ports that send us LOGO

After a quick link flap, a target was seen to send us a LOGO.
Apparently, it saw an RSCN reporting that we had dropped out of the
fabric after we had logged back into it.

This is likely in larger fabrics (more than 2 FC switches) after
a quick link flap at the initiator.  Each link transition causes
an port-specific RSCN to the target.  After the link comes back up,
the initiator successfully discovers and does a PLOGI to the target
before the target sees the first RSCN reporting the initiator is gone,
and it sends a LOGO.  The target may see a subsequent RSCN saying the
port is back, but probably wouldn't send a PLOGI and leaves it
up to the initiator to re-login.

An RSCN can be delayed by the switches due to software layers but a
PLOGI is forwarded in hardware causing the PLOGI to beat the RSCN.

If a remote port is in the discovered set and sends a LOGO, re-login to it.

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@suse.de>