app/testpmd: add MPLSoUDP encapsulation

app/testpmd: add MPLSoUDP encapsulation

MPLSoUDP is an example for L3 tunnel encapsulation.

L3 tunnel type is a tunnel that is missing the layer 2 header of the
inner packet.

Example for MPLSoUDP tunnel:
ETH / IPV4 / UDP / MPLS / IP / L4..L7

In order to encapsulate such a tunnel there is a need to remove L2 of
the inner packet and encap the remaining tunnel, this is done by
applying 2 rte flow commands l2_decap followed by mplsoudp_encap.
Both commands must appear in the same flow, and from the point of the
packet it both actions are applied at the same time. (There is no part
where a packet doesn't have L2 header).

Decapsulating such a tunnel works the other way, first we need to decap
the outer tunnel header and then apply the new L2.
So the commands will be mplsoudp_decap / l2_encap

Due to the complex encapsulation of MPLSoUDP and L2  flow actions and
based on the fact testpmd does not allocate memory, this patch adds a
new command in testpmd to initialise a global structures containing the
necessary information to make the outer layer of the packet.  This same
global structures will then be used by the flow commands in testpmd when
the action mplsoudp_encap, mplsoudp_decap, l2_encap, l2_decap, will be
parsed, at this point, the conversion into such action becomes trivial.

The l2_encap and l2_decap actions can also be used for other L3 tunnel
types.

Signed-off-by: Ori Kam <orika@mellanox.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>