net: cosmetic: Fix var naming net <-> eth drivers

Update the naming convention used in the network stack functions and
variables that Ethernet drivers use to interact with it.

This cleans up the temporary hacks that were added to this interface
along with the DM support.

This patch has a few remaining checkpatch.pl failures that would be out
of the scope of this patch to fix (drivers that are in gross violation
of checkpatch.pl).

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>