mcx(4) on OpenBSD

The text 6ef1c9e1aefe, as OpenBSD 7.3, OpenBSD 7.2, OpenBSD 7.1, OpenBSD 7.0, OpenBSD 6.9, OpenBSD 6.8, OpenBSD 6.7, OpenBSD 6.6 shipped it.

Mellanox 5th generation Ethernet device