feat: option to specify netlink header flags in LinkAddRequest

[richardstephens]

We're trying to enable vlan_filtering on an existing bridge, the equivalant of

# ip link set dev br0 type bridge vlan_filtering 1

After some back and forth manipulating the message and strace'ing iproute2 to eliminate all the differences, I got to the point where the only difference was that the flags used by iproute2 were NLM_F_REQUEST|NLM_F_ACK.

With this change, we are now able to successfully enable vlan filtering on a bridge like so:

    let (link_index, _) = find_link(&handle, "br0".to_string())
        .await
        .unwrap()
        .unwrap();

    let mut req: LinkAddRequest = handle.link().add().flags(0);
    let mut msg = req.message_mut();
    msg.header.index = link_index;
    msg.attributes.push(LinkAttribute::LinkInfo(vec![
        LinkInfo::Kind(InfoKind::Bridge),
        LinkInfo::Data(InfoData::Bridge(vec![InfoBridge::VlanFiltering(1)])),
    ]));
    req.execute().await.unwrap();

Questions

• Does modifying LinkAddRequest to support sending these types of requests make sense? Perhaps a new Link...Request might be more appropriate
• Might exposing this functionality in other request types also be helpful?

[cathay4t]

Thanks for the contribution!

We are in the middle of design discussion on how we should handle this kind of requests at #57

Could you wait a little bit or even better join our discussion there?