veth: Handle flags correctry

Flags for a peer override flags for the other and not used for the
peer.

before:
# ip link add up type veth peer down multicast off
# ip link
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: veth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 2e:5c:cd:f5:63:d2 brd ff:ff:ff:ff:ff:ff
3: veth1: <BROADCAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 72:b0:fa:1e:76:7a brd ff:ff:ff:ff:ff:ff

after:
# ip link add up type veth peer down multicast off
# ip link
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: veth0: <BROADCAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 6e:db:03:b3:bd:ff brd ff:ff:ff:ff:ff:ff
3: veth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether a6:62:d9:84:f0:73 brd ff:ff:ff:ff:ff:ff
Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>

ip/link_veth.c

@@ -34,12 +34,20 @@ static int veth_parse_opt(struct link_util *lu, int argc, char **argv,
 	int err, len;
 	struct rtattr * data;
 	int group;
+	struct ifinfomsg *ifm, *peer_ifm;
+	unsigned int ifi_flags, ifi_change;
 
 	if (strcmp(argv[0], "peer") != 0) {
 		usage();
 		return -1;
 	}
 
+	ifm = NLMSG_DATA(hdr);
+	ifi_flags = ifm->ifi_flags;
+	ifi_change = ifm->ifi_change;
+	ifm->ifi_flags = 0;
+	ifm->ifi_change = 0;
+
 	data = NLMSG_TAIL(hdr);
 	addattr_l(hdr, 1024, VETH_INFO_PEER, NULL, 0);
 
@@ -57,10 +65,12 @@ static int veth_parse_opt(struct link_util *lu, int argc, char **argv,
 		addattr_l(hdr, 1024, IFLA_IFNAME, name, len);
 	}
 
-	if (index) {
-		struct ifinfomsg *ifi = (struct ifinfomsg *)(data + 1);
-		ifi->ifi_index = index;
-	}
+	peer_ifm = RTA_DATA(data);
+	peer_ifm->ifi_index = index;
+	peer_ifm->ifi_flags = ifm->ifi_flags;
+	peer_ifm->ifi_change = ifm->ifi_change;
+	ifm->ifi_flags = ifi_flags;
+	ifm->ifi_change = ifi_change;
 
 	if (group != -1)
 		addattr32(hdr, 1024, IFLA_GROUP, group);