Order fields to increase locality for most used protocols.

udplite and icmp are moved at the end.

Same for proc_net_devsnmp6 which is not used in fast path.

This potentially saves one cache line miss for typical TCP/UDP over IPv4/IPv6.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>