Loopback Amigaos4

SANA-II software loopback.device for AmigaOS 4 — every CMD_WRITE is delivered back to every opener's CMD_READ, no PCI/DMA/QEMU roundtrip in the path. A diagnostic instrument for measuring the bsdsocket + Roadshow + SANA-II stack ceiling in isolation. Working; ~19 Mbit/s at 1500-byte frames on QEMU sam460ex.