Reimplement linux/samples xdp programs in P4

[fruffy]

A nice way to show the usefulness of the compiler is to reimplement most of the xdp examples in the /linux/samples folder in pure P4 code.
This is also a good way to determine discrepancies or detect missing features.

[williamtu]

I think we have one, which does the MAC address swapping and return XDP_TX

[williamtu]

I think we have one, which does the MAC address swapping and return XDP_TX

[fruffy]

Ha yes, I actually got the idea when reading the performance section in the paper. It is a
neat comparison.