Suricata, Jumbo Frames, and netmap

One of my FreeBSD machines sits between the Internet and the rest of my network.
I wanted Suricata to monitor traffic arriving on four of the machine's interfaces and complain when something looks wrong.
I started with one interface, `mce1`, and planned to add the other three after capture worked.
The capture interfaces are backed by Mellanox ConnectX adapters handled by the mlx5en driver, and they use a jumbo-frame MTU of 9000 bytes.