[NET]: Annotate h_proto in struct ethhdr

The protocol field in ethernet headers is big-endian and should be
annotated as such.  This patch allows detection of missing ntohs() calls
on the ethernet protocol field when sparse is run with __CHECK_ENDIAN__
defined.

This is a revised version that includes <linux/types.h> so that the
userspace programs are not confused by __be16.  Thanks to David S.
Miller.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: David S. Miller <davem@davemloft.net>