coverage support is module-centric

[alan-maguire]

support for enabling coverage/memory tracking is currently only done on a per-module basis which is useful for some consumers, but for core kernel components like sk_buff interfaces we probably want to have the notion of collecting coverage information on a per-API basis. So idea would be we could enable coverage for multiple functions under the umbrella of a single API, e.g.

ktfcov -e sk_buff/alloc_skb ktfcov -e sk_buff/kfree_skb

etc. We would then collect/record entry/memory data on a per-API basis in a similar way to how we do this on a per-module basis. It would be nice if we could auto-extract such an API list from the relevant header file.