Does not retry for mavlink connection

[fnoop]

If you start the mavcesium standalone server before the mavlink connection is ready (eg. mavlink proxy is not yet fully started), it does not seem to retry and reconnect when the mavlink connection does become available.

In particular I'm testing this on the Maverick 1.1.5 release for Tegra TX1. On boot the mavcesium service starts slighty before or at the same time as mavlink-router@sitl service. The mavlink proxy (mavlink-router@sitl) service does start up very shortly afterwards and is available, however you have to restart mavcesium service before it connects. It should retry connection.

[SamuelDudley]

Should be an easy fix! I'll add retry by default and add an opt out launch option.