ncsi: Create Interface type to wrap a network interface instance

Define an interface as a new type, just containing the ifindex
currently.

This will allow future Interface implementations that don't interact
directly with a local Linux network interface.

Tested: "get info" (--info) and "send OEM command" (--oem-payload)
operations tested against kernel NCSI layer, to a test NC-SI device.

Change-Id: If0471ac3fa41e08bb916e9279d4fe5b668860b03
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
3 files changed