Restructure IbusMsg

[Paul-weqe]

IbusMsg had too many items (which can only keep growing). This commit restructures
the actions and categorize each item e.g Interface/RouteId and actions like add, delete,
update etc...

[Paul-weqe]

@rwestphal tests failing with an issue from the BGP tests. Can you help with that ?

[rwestphal]

Love this!

One thing we could do is derive EnumAsInner for the IbusMsg enum, which would let us leverage the From trait like this:

Instead of:

    let msg = IbusMsg::RouteMpls(RouteMplsMsg::Add(msg));
    let _ = ibus_tx.send(msg);

We could simplify it to:

    let msg = RouteMplsMsg::Add(msg);
    let _ = ibus_tx.send(msg.into());

@rwestphal tests failing with an issue from the BGP tests. Can you help with that ?

Our data-driven test framework uses JSON data to represent event messages, including ibus messages. By changing the IbusMsg enum, we need to regenerate all the test topologies data (which can be done automatically with a single command). Some conformance tests will need to be updated manually though, but only for input events. Since I'll be traveling in a couple of days, let's hold off on this for now.

[Paul-weqe]

@rwestphal are you talking about manually implementing the From trait on the enums ?

Looking through the enum-as-inner docs and testing locally. Finding it difficult to see a way we can run let _ = ibus_tx.send(msg.into()); without implementing the trait ourselves.

[rwestphal]

@Paul-weqe You're absolutely right. The enum-as-inner crate only handles the conversion from the enum type to its variants, but not the other way around. But we can possibly use the derive-more crate to avoid implementing those conversions manually. The less code we need to write, the better.