We had this for the old style in-flight spawns, but not for mid-mission
spawns. Aircraft that were spawning soon after takeoff could potentially
be close to (or under) the ground, causing them to "crash" at game
start. The altitude is different here than for the old style in-flight
spawns to try to get closer to the intended spawn location.
Fixes https://github.com/dcs-liberation/dcs_liberation/issues/1941