ekf2: add fake height fusion logic

When there is no vertical aiding, fake height is started to constrain
the vertical channel of the EKF

src/modules/ekf2/EKF/common.h

@@ -533,6 +533,7 @@ union filter_control_status_u {
 		uint64_t wind_dead_reckoning     : 1; ///< 30 - true if we are navigationg reliant on wind relative measurements
 		uint64_t rng_kin_consistent      : 1; ///< 31 - true when the range finder kinematic consistency check is passing
 		uint64_t fake_pos                : 1; ///< 32 - true when fake position measurements are being fused
+		uint64_t fake_hgt                : 1; ///< 33 - true when fake height measurements are being fused
 	} flags;
 	uint64_t value;
 };