sample: DPDK packet forwarder + Docker CI

[benaadams]

Problem

DPDK needs a sample application and CI infrastructure to validate it works.

Sub-tasks

• Create sample/Magma.DPDK.PacketForwarder - L2 forwarding between two ports
• Docker Compose with DPDK, veth pair or null PMD
• README: prerequisites, huge page setup, NIC binding
• CI job using Docker DPDK image

Dependencies

Depends on: #128
Unlocks: platform I/O benchmarks (#TBD), demonstrates the DPDK integration

Phase

Phase 3 (Advanced Integrations)