mavlink: create stream if needed and trigger once
mavlink: create stream if needed and trigger once

Instead of creating the stream and deleting it again, we now create it
with a rate of 0 and trigger it once.

This should avoid heap fragmentation by continous allocations.

acfloria/Firmware,acfloria/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,PX4/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware