Add a test suite for the AVB (Audio Video Bridging) protocol stack that
runs entirely in software, requiring no hardware, root privileges, or
running PipeWire daemon.
The loopback transport (avb-transport-loopback.h) replaces raw AF_PACKET
sockets with in-memory packet capture, using a synthetic MAC address and
eventfd for protocol handlers that need a valid fd.
Test utilities (test-avb-utils.h) provide helpers for creating test
servers, injecting packets, advancing time, and building ADP packets.
Tests cover:
- ADP entity available/departing/discover/timeout
- MRP attribute lifecycle (create, begin, join)
- Milan v1.2 mode server creation
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
