use the proper check to prevent multiple mavlink instances on the same udp port, added warning when different remote than localhost connects to udp

added takeoff logic for position controller to get the uav off the ground fast and transition smoothly to poctl after takeoff, added landing logic to reduce thrust to zero once on the ground

correct thrust limiting during landing with margin, don't reset position setpoint when switching from takeoff to posctl and allow high enough z velocity for position lock

in mc auto: do not reset the position sp while near the waypoint, should make switching to manual pos control smoother