[SCSI] libfc: make rport module maintain the rport list

The list of remote ports (struct fc_rport_priv) has been
maintained by the discovery module.  In preparation for having
lport->tt.rport_create() do a lookup first, maintain the
rports list in the rport module.  It will still be protected
by the disc_mutex.

The DNS rport is an exception for until after further patches.
For now, do not add it to the list.

The point-to-point rport will be in the discovery list.
So at shutdown, it doesn't need to be separately logged out.

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>