Move setting up addresses for a container, into weaveutil-invoked function

This means we only change netns by execing nsenter: changing netns in
Go is unsafe for long-running processes like the proxy.

prog/weaveutil/main.go

@@ -32,6 +32,7 @@ func init() {
 		"check-iface":              checkIface,
 		"del-iface":                delIface,
 		"setup-iface":              setupIface,
+		"setup-iface-addrs":        setupIfaceAddrs,
 		"list-netdevs":             listNetDevs,
 		"cni-net":                  cniNet,
 		"cni-ipam":                 cniIPAM,

prog/weaveutil/netdev.go

@@ -50,6 +50,26 @@ func setupIface(args []string) error {
 	return weavenet.SetupIface(ifaceName, newIfName)
 }
 
+// setupIfaceAddrs sets up addresses on an interface. It expects to be called inside the container's netns.
+func setupIfaceAddrs(args []string) error {
+	if len(args) < 1 {
+		cmdUsage("setup-iface-addrs", "<iface-name> <with-multicast> <cidr>...")
+	}
+	link, err := netlink.LinkByName(args[0])
+	if err != nil {
+		return err
+	}
+	withMulticastRoute, err := strconv.ParseBool(args[1])
+	if err != nil {
+		return err
+	}
+	cidrs, err := parseCIDRs(args[2:])
+	if err != nil {
+		return err
+	}
+	return weavenet.SetupIfaceAddrs(link, withMulticastRoute, cidrs)
+}
+
 func configureARP(args []string) error {
 	if len(args) != 2 {
 		cmdUsage("configure-arp", "<iface-name-prefix> <root-path>")