Upstream vale port type extraction

[garrettkajmowicz-sophos]

Adds some logic which we have found to be useful. Namely, provide a way to determine what type of VALE port we are dealing with. This is useful to identify configuration issues or to be able to take different actions based on where the data is coming from.

[vmaffione]

This is legacy API, and therefore can't be changed.

[vmaffione]

Shouldn't we distinguish between ephemeral vale ports and persistent vale ports (e.g. created with vale-ctl -n?)

[vmaffione]

Hi,
We discussed with @giuseppelettieri , and we think it is necessary to change the approach to play with this kind of port-type information.
Trying to recover the port type by peeking inside pointers of the netmap adapters is very fragile (w.r.t. changes) and unnecessarily complex. Also, we should make this mechanism more generic, and make it possible to recover the port-type also for non-VALE ports.

A better approach is to add an adapter_type or port_type enum field to the struct netmap_adapter, so that any netmap port has a port type. The adapter_type field is set when the netmap adapter struct is created. This may be netmap_attach for NIC ports, netmap_get_null_na for null ports, netmap_get_pipe_na for pipe ports, etc. You can look at the netmap_get_na function to see all the ports that we support.

Once we do this, we can extend the struct nmreq_port_info_get to retrieve the additional adaper_type field. We can also add this field to struct nmreq_vale_list, as your original change did.