gre: add support for collect metadata flag

This patch add support for IFLA_GRE_COLLECT_METADATA via the
'external' keyword to the gre link.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

ip/link_gre.c

@@ -74,6 +74,7 @@ static int gre_parse_opt(struct link_util *lu, int argc, char **argv,
 	__u16 encapflags = 0;
 	__u16 encapsport = 0;
 	__u16 encapdport = 0;
+	__u8 metadata = 0;
 
 	if (!(n->nlmsg_flags & NLM_F_CREATE)) {
 		memset(&req, 0, sizeof(req));
@@ -148,6 +149,9 @@ get_failed:
 			encapsport = rta_getattr_u16(greinfo[IFLA_GRE_ENCAP_SPORT]);
 		if (greinfo[IFLA_GRE_ENCAP_DPORT])
 			encapdport = rta_getattr_u16(greinfo[IFLA_GRE_ENCAP_DPORT]);
+
+		if (greinfo[IFLA_GRE_COLLECT_METADATA])
+			metadata = 1;
 	}
 
 	while (argc > 0) {
@@ -291,6 +295,8 @@ get_failed:
 			encapflags |= TUNNEL_ENCAP_FLAG_REMCSUM;
 		} else if (strcmp(*argv, "noencap-remcsum") == 0) {
 			encapflags |= ~TUNNEL_ENCAP_FLAG_REMCSUM;
+		} else if (strcmp(*argv, "external") == 0) {
+			metadata = 1;
 		} else
 			usage();
 		argc--; argv++;
@@ -325,6 +331,8 @@ get_failed:
 	addattr16(n, 1024, IFLA_GRE_ENCAP_FLAGS, encapflags);
 	addattr16(n, 1024, IFLA_GRE_ENCAP_SPORT, htons(encapsport));
 	addattr16(n, 1024, IFLA_GRE_ENCAP_DPORT, htons(encapdport));
+	if (metadata)
+		addattr_l(n, 1024, IFLA_GRE_COLLECT_METADATA, NULL, 0);
 
 	return 0;
 }
@@ -413,6 +421,9 @@ static void gre_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
 	if (oflags & GRE_CSUM)
 		fputs("ocsum ", f);
 
+	if (tb[IFLA_GRE_COLLECT_METADATA])
+		fputs("external ", f);
+
 	if (tb[IFLA_GRE_ENCAP_TYPE] &&
 	    *(__u16 *)RTA_DATA(tb[IFLA_GRE_ENCAP_TYPE]) != TUNNEL_ENCAP_NONE) {
 		__u16 type = rta_getattr_u16(tb[IFLA_GRE_ENCAP_TYPE]);