vxlan: Follow kernel defaults for outer UDP checksum.

On recent kernels, UDP checksum computation has become more efficient and
the default behavior was changed, however, the ip command overrides this
by always specifying a particular behavior.

If the user does not specify that UDP checksums should either be computed
or not then we don't need to send an explicit netlink message - the kernel
can just use its default behavior.
Signed-off-by: Jesse Gross <jesse@kernel.org>

ip/iplink_vxlan.c

@@ -68,8 +68,11 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 	__u32 maxaddr = 0;
 	__u16 dstport = 0;
 	__u8 udpcsum = 0;
+	bool udpcsum_set = false;
 	__u8 udp6zerocsumtx = 0;
+	bool udp6zerocsumtx_set = false;
 	__u8 udp6zerocsumrx = 0;
+	bool udp6zerocsumrx_set = false;
 	__u8 remcsumtx = 0;
 	__u8 remcsumrx = 0;
 	__u8 metadata = 0;
@@ -194,16 +197,22 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 			l3miss = 1;
 		} else if (!matches(*argv, "udpcsum")) {
 			udpcsum = 1;
+			udpcsum_set = true;
 		} else if (!matches(*argv, "noudpcsum")) {
 			udpcsum = 0;
+			udpcsum_set = true;
 		} else if (!matches(*argv, "udp6zerocsumtx")) {
 			udp6zerocsumtx = 1;
+			udp6zerocsumtx_set = true;
 		} else if (!matches(*argv, "noudp6zerocsumtx")) {
 			udp6zerocsumtx = 0;
+			udp6zerocsumtx_set = true;
 		} else if (!matches(*argv, "udp6zerocsumrx")) {
 			udp6zerocsumrx = 1;
+			udp6zerocsumrx_set = true;
 		} else if (!matches(*argv, "noudp6zerocsumrx")) {
 			udp6zerocsumrx = 0;
+			udp6zerocsumrx_set = true;
 		} else if (!matches(*argv, "remcsumtx")) {
 			remcsumtx = 1;
 		} else if (!matches(*argv, "noremcsumtx")) {
@@ -278,13 +287,16 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 	addattr8(n, 1024, IFLA_VXLAN_RSC, rsc);
 	addattr8(n, 1024, IFLA_VXLAN_L2MISS, l2miss);
 	addattr8(n, 1024, IFLA_VXLAN_L3MISS, l3miss);
-	addattr8(n, 1024, IFLA_VXLAN_UDP_CSUM, udpcsum);
-	addattr8(n, 1024, IFLA_VXLAN_UDP_ZERO_CSUM6_TX, udp6zerocsumtx);
-	addattr8(n, 1024, IFLA_VXLAN_UDP_ZERO_CSUM6_RX, udp6zerocsumrx);
 	addattr8(n, 1024, IFLA_VXLAN_REMCSUM_TX, remcsumtx);
 	addattr8(n, 1024, IFLA_VXLAN_REMCSUM_RX, remcsumrx);
 	addattr8(n, 1024, IFLA_VXLAN_COLLECT_METADATA, metadata);
 
+	if (udpcsum_set)
+		addattr8(n, 1024, IFLA_VXLAN_UDP_CSUM, udpcsum);
+	if (udp6zerocsumtx_set)
+		addattr8(n, 1024, IFLA_VXLAN_UDP_ZERO_CSUM6_TX, udp6zerocsumtx);
+	if (udp6zerocsumrx_set)
+		addattr8(n, 1024, IFLA_VXLAN_UDP_ZERO_CSUM6_RX, udp6zerocsumrx);
 	if (noage)
 		addattr32(n, 1024, IFLA_VXLAN_AGEING, 0);
 	else if (age)
@@ -426,16 +438,23 @@ static void vxlan_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
 	    ((maxaddr = rta_getattr_u32(tb[IFLA_VXLAN_LIMIT])) != 0))
 		    fprintf(f, "maxaddr %u ", maxaddr);
 
-	if (tb[IFLA_VXLAN_UDP_CSUM] && rta_getattr_u8(tb[IFLA_VXLAN_UDP_CSUM]))
+	if (tb[IFLA_VXLAN_UDP_CSUM]) {
+		if (!rta_getattr_u8(tb[IFLA_VXLAN_UDP_CSUM]))
+			fputs("no", f);
 		fputs("udpcsum ", f);
+	}
 
-	if (tb[IFLA_VXLAN_UDP_ZERO_CSUM6_TX] &&
-	    rta_getattr_u8(tb[IFLA_VXLAN_UDP_ZERO_CSUM6_TX]))
+	if (tb[IFLA_VXLAN_UDP_ZERO_CSUM6_TX]) {
+		if (!rta_getattr_u8(tb[IFLA_VXLAN_UDP_ZERO_CSUM6_TX]))
+			fputs("no", f);
 		fputs("udp6zerocsumtx ", f);
+	}
 
-	if (tb[IFLA_VXLAN_UDP_ZERO_CSUM6_RX] &&
-	    rta_getattr_u8(tb[IFLA_VXLAN_UDP_ZERO_CSUM6_RX]))
+	if (tb[IFLA_VXLAN_UDP_ZERO_CSUM6_RX]) {
+		if (!rta_getattr_u8(tb[IFLA_VXLAN_UDP_ZERO_CSUM6_RX]))
+			fputs("no", f);
 		fputs("udp6zerocsumrx ", f);
+	}
 
 	if (tb[IFLA_VXLAN_REMCSUM_TX] &&
 	    rta_getattr_u8(tb[IFLA_VXLAN_REMCSUM_TX]))