ethdev: add transfer attribute to flow API

ethdev: add transfer attribute to flow API

This new attribute enables applications to create flow rules that do not
simply match traffic whose origin is specified in the pattern (e.g. some
non-default physical port or VF), but actively affect it by applying the
flow rule at the lowest possible level in the underlying device.

It breaks ABI compatibility for the following public functions:

- rte_flow_copy()
- rte_flow_create()
- rte_flow_validate()

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>