Fix buildIpamResources()

- Can no longer assume IPv6 operational data to be present

Signed-off-by: Alessandro Boch <aboch@docker.com>

api/server/router/network/network_routes.go

@@ -264,6 +264,9 @@ func buildIpamResources(r *types.NetworkResource, nwInfo libnetwork.NetworkInfo)
 
 	if !hasIpv6Conf {
 		for _, ip6Info := range ipv6Info {
+			if ip6Info.IPAMData.Pool == nil {
+				continue
+			}
 			iData := network.IPAMConfig{}
 			iData.Subnet = ip6Info.IPAMData.Pool.String()
 			iData.Gateway = ip6Info.IPAMData.Gateway.String()