sfc: move common rx code

The moved code deals with managing rx buffers and queues.
A tiny bit of refactoring was required in other files to stitch the
code together.

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