[NET]: Make skb->protocol __be16

There are many instances of

	skb->protocol = htons(ETH_P_*);
	skb->protocol = __constant_htons(ETH_P_*);
and
	skb->protocol = *_type_trans(...);

Most of *_type_trans() are already endian-annotated, so, let's shift
attention on other warnings.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>