Add function cTab_fnc_unitInEnabledVehicleSeat to check if a unit is in the right seat of a FBCB2 or TAD enabled vehicle. This fixes a incompatibility with Konyo's Boeing/SOAR MH-47E mod (left door gunner would have TAD instead of co-pilot).
Fixes that  players riding in the back of the large trucks had access to FBCB2.