net: display more skb fields in skb_dump()

Print these additional fields in skb_dump() to ease debugging.

- mac_len
- csum_start (in v2, at Willem suggestion)
- csum_offset (in v2, at Willem suggestion)
- priority
- mark
- alloc_cpu
- vlan_all
- encapsulation
- inner_protocol
- inner_mac_header
- inner_network_header
- inner_transport_header

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>