Force mavlink 1.0 until 2.0 is verified as a valid option

Oct 06 18:23
@tridge mavproxy is failing against Solo without passing in "--mav10". Gets telemetry but Solo doesn't respond to commands. I believe we should fall back to sending 1.0 if we receive 1.0 on a link, shouldn't we?

08:13
@peterbarker yes, we should. We need to teach mavproxy to set force_mavlink1 until it knows the server can handle mavlink2, either by seeing a mavlink2 pkt or by requesting AUTOPILOT_VERSION and checking capabilities

Start by tracing MAVProxy's MAVLink version handling around the --mav10 option and the proposed force_mavlink1 state. Check how incoming MAVLink 1.0 packets and AUTOPILOT_VERSION capability responses are processed. Done means a link that reports or only uses MAVLink 1.0 remains compatible, while MAVLink 2.0 is used only after it is verified.

Written by the indexing model from the issue text.