Force disarm of copter by sending DISARM command with param2 with 21196

AC3.2.1 and AC3.3 require the vehicle to be landed before the vehicle will accept a disarm request.
AC3.3 will accept the disarm however (regardless of whether the vehicle is landed or not) if param 2 is set to 21196

No files or tests are identified. Start by locating Mission Planner's disarm command handling and the code that builds the vehicle command parameters; verify how AC3.2.1 and AC3.3 respond, then confirm that the requested DISARM behavior uses param2 value 21196 and works for the stated vehicle versions.

Written by the indexing model from the issue text.