ip_tunnels: remove custom alignment and packing

The custom alignment of struct ip_tunnel_key is unnecessary. In struct
sw_flow_key, it starts at offset 256, in struct ip_tunnel_info it's the
first field.

The structure is also packed even without the __packed keyword.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>