MPLS Switching

This PR implements a very simple form of MPLS-Switching in P4. It demonstrates how one could implement a custom protocol using P4. This example works by appending a custom header based on the destination IP address and then performing routing based on it.

The label gets removed based on a table entry when the packet is about to arrive at a switch connected to hosts.

Topology used in this Example

graph LR
	A[h1] --- B[s1]
	C[h2] --- B[s1]
	B[s1] --- D[s2]
	B[s1] --- E[s4]
	D[s2] --- F[s3]
	F[s3] --- G[h3]
	E[s4] --- G[s5]
	G[s5] --- H[h3]