sfc: move some channel-related code

Just a handful of function, but also removed many 'static' identifiers
so the code builds. These will, of course, be moved.
Module parameters for IRQ moderation threshold also moved.

Small code styling fixes included.

Signed-off-by: Alexandru-Mihai Maftei <amaftei@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>