Parameter download stalls if MinimOSD or other mavlink device connected

It appears MP is trying to download parameters from any mavlink device that is connected.

We certainly want to download parameters from all vehicles but some devices (perhaps most devices) won't respond to requests for parameters. I'm not sure how we can distinguish between devices that can and cannot respond.

Start by reproducing the parameter download with a vehicle and a MinimOSD or other nonresponsive MAVLink device connected, then trace which device receives parameter requests. Done means vehicle parameter downloads complete without stalling when another connected device does not respond.

Written by the indexing model from the issue text.