[SCSI] libfc: Handle unsolicited PRLO request

Resubmitting after incorporating Joe's review comment.

Unsolicited PRLO request is now handled by sending LS_ACC,
and then relogin to the remote port if an N-port login
session exists for that remote port.

Note that this patch should be applied on top of Joe Eykholt's
"Fix remote port restart problem" patch.

Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

include/scsi/fc/fc_els.h

@@ -404,6 +404,15 @@ struct fc_els_prli {
 	/* service parameter pages follow */
 };
 
+/*
+ * ELS_PRLO - Process logout request and response.
+ */
+struct fc_els_prlo {
+	__u8            prlo_cmd;       /* command */
+	__u8            prlo_obs;       /* obsolete, but shall be set to 10h */
+	__be16          prlo_len;       /* payload length */
+};
+
 /*
  * ELS_ADISC payload
  */