ethdev: add raw encapsulation action

ethdev: add raw encapsulation action

Currenlty the encap/decap actions only support encapsulation
of VXLAN and NVGRE L2 packets (L2 encapsulation is where
the inner packet has a valid Ethernet header, while L3 encapsulation
is where the inner packet doesn't have the Ethernet header).
In addtion the parameter to to the encap action is a list of rte items,
this results in 2 extra translation, between the application to the
actioni and from the action to the NIC. This results in negative impact
on the insertion performance.

Looking forward there are going to be a need to support many more tunnel
encapsulations. For example MPLSoGRE, MPLSoUDP.
Adding the new encapsulation will result in duplication of code.
For example the code for handling NVGRE and VXLAN are exactly the same,
and each new tunnel will have the same exact structure.

This patch introduce a raw encapsulation that can support L2 tunnel types
and L3 tunnel types. In addtion the new
encapsulations commands are using raw buffer inorder to save the
converstion time, both for the application and the PMD.

In order to encapsulate L3 tunnel type there is a need to use both
actions in the same rule: The decap to remove the L2 of the original
packet, and then encap command to encapsulate the packet with the
tunnel.
For decap L3 there is also a need to use both commands in the same flow
first the decap command to remove the outer tunnel header and then encap
to add the L2 header.

Signed-off-by: Ori Kam <orika@mellanox.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>