mpls: Use definition for reserved label checks

In multiple locations there are checks for whether the label in hand
is a reserved label or not using the arbritray value of 16. Factor
this out into a #define for better maintainability and for
documentation.

Signed-off-by: Robert Shearman <[e-mail]>
Acked-by: Roopa Prabhu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/mpls.h

···
 #define MPLS_LABEL_OAMALERT		14 /* RFC3429 */
 #define MPLS_LABEL_EXTENSION		15 /* RFC7274 */
 
+#define MPLS_LABEL_FIRST_UNRESERVED	16 /* RFC3032 */
+
 #endif /* _UAPI_MPLS_H */

net/mpls/af_mpls.c

···
 	struct mpls_route *rt = new ? new : old;
 	unsigned nlm_flags = (old && new) ? NLM_F_REPLACE : 0;
 	/* Ignore reserved labels for now */
-	if (rt && (index >= 16))
+	if (rt && (index >= MPLS_LABEL_FIRST_UNRESERVED))
 		rtmsg_lfib(event, index, rt, nlh, net, portid, nlm_flags);
 }
 
···
 
 	platform_label = rtnl_dereference(net->mpls.platform_label);
 	platform_labels = net->mpls.platform_labels;
-	for (index = 16; index < platform_labels; index++) {
+	for (index = MPLS_LABEL_FIRST_UNRESERVED; index < platform_labels;
+	     index++) {
 		if (!rtnl_dereference(platform_label[index]))
 			return index;
 	}
···
 		index = find_free_label(net);
 	}
 
-	/* The first 16 labels are reserved, and may not be set */
-	if (index < 16)
+	/* Reserved labels may not be set */
+	if (index < MPLS_LABEL_FIRST_UNRESERVED)
 		goto errout;
 
 	/* The full 20 bit range may not be supported. */
···
 
 	index = cfg->rc_label;
 
-	/* The first 16 labels are reserved, and may not be removed */
-	if (index < 16)
+	/* Reserved labels may not be removed */
+	if (index < MPLS_LABEL_FIRST_UNRESERVED)
 		goto errout;
 
 	/* The full 20 bit range may not be supported */
···
 					   &cfg->rc_label))
 				goto errout;
 
-			/* The first 16 labels are reserved, and may not be set */
-			if (cfg->rc_label < 16)
+			/* Reserved labels may not be set */
+			if (cfg->rc_label < MPLS_LABEL_FIRST_UNRESERVED)
 				goto errout;
 
 			break;
···
 	ASSERT_RTNL();
 
 	index = cb->args[0];
-	if (index < 16)
-		index = 16;
+	if (index < MPLS_LABEL_FIRST_UNRESERVED)
+		index = MPLS_LABEL_FIRST_UNRESERVED;
 
 	platform_label = rtnl_dereference(net->mpls.platform_label);
 	platform_labels = net->mpls.platform_labels;