Currently, psample can only send the packet bits after decapsulation.
The tunnel information is lost. Add the tunnel support.

If the sampled packet has no tunnel info, the behavior is the same as
before. If it has, add a nested metadata field named PSAMPLE_ATTR_TUNNEL
and include the tunnel subfields if applicable.

Increase the metadata length for sampled packet with the tunnel info.
If new subfields of tunnel info should be included, update the metadata
length accordingly.
Signed-off-by: Chris Mi <chrism@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>