[RFC] struct stream_sock (aka struct sock shrink-me-harder)

Hi Dave,

	It compiles, boots, survives some testing, but is incomplete yet in
the old protos that I have to convert to per protocol slabcaches, which will
also allow us to get rid of sk_protinfo.

	Some cases are more tricky, like bluetooth, that uses both per
protocol slabcache _and_ sk->sk_protinfo, probably the best thing to do in
this case is to make bluetooth use sk->sk_prot, and that is what I plan
to do eventually to all families, to get rid of sk->sk_slab (i.e. when
all families use sk->sk_prot we can just use sk->sk_prot->slab).

	I think that besides the savings per struct sock instance on
non stream/seqpacket protos this makes things clearer by separating the
stream stuff from the bare struct sock that is needed for all familes.

	Anyway, what do you think? Any member in struct stream_sock that
should not have been moved from struct sock?

Best Regards,

- Arnaldo