Necessary because NuttX defines pollfd differend from
the POSIX standard. The difference of field order makes
use of C++ designated initializers to compile for both
platforms impossible.

If the landed state was set before the position controller starts it
would get updated with the first poll_subscriptions() anyways. But it's
not on all posix and nuttx platforms I tested and the deleted statement
just copies the zero message into the struct which is already zero.

 - fixes #10925

FlightTaskAutoLine: ensure that desired speed along track does not exceed maximum speed at threshold to target

Smoothing can be configured by MPC_POS_MODE parameter
put before only for position mode and not for altitude mode.