ekf2: allow sideslip fusion to always start with airspeed fusion

This allow sideslip fusion to start during VTOL front transition or even
on a multirotor with a vertical stabilizer and an airspeed sensor for example.

src/modules/ekf2/EKF/aid_sources/sideslip/sideslip_fusion.cpp

@@ -50,7 +50,7 @@
 void Ekf::controlBetaFusion(const imuSample &imu_delayed)
 {
 	_control_status.flags.fuse_beta = _params.beta_fusion_enabled
-					  && _control_status.flags.fixed_wing
+					  && (_control_status.flags.fixed_wing || _control_status.flags.fuse_aspd)
 					  && _control_status.flags.in_air
 					  && !_control_status.flags.fake_pos;
 

src/modules/ekf2/EKF2.hpp

@@ -573,12 +573,9 @@ private:
 #endif // CONFIG_EKF2_AIRSPEED
 
 #if defined(CONFIG_EKF2_SIDESLIP)
-		(ParamExtFloat<px4::params::EKF2_BETA_GATE>)
-		_param_ekf2_beta_gate, ///< synthetic sideslip innovation consistency gate size (STD)
-		(ParamExtFloat<px4::params::EKF2_BETA_NOISE>) _param_ekf2_beta_noise, ///< synthetic sideslip noise (rad)
-
-		(ParamExtInt<px4::params::EKF2_FUSE_BETA>)
-		_param_ekf2_fuse_beta, ///< Controls synthetic sideslip fusion, 0 disables, 1 enables
+		(ParamExtFloat<px4::params::EKF2_BETA_GATE>) _param_ekf2_beta_gate,
+		(ParamExtFloat<px4::params::EKF2_BETA_NOISE>) _param_ekf2_beta_noise,
+		(ParamExtInt<px4::params::EKF2_FUSE_BETA>) _param_ekf2_fuse_beta,
 #endif // CONFIG_EKF2_SIDESLIP
 
 #if defined(CONFIG_EKF2_MAGNETOMETER)

src/modules/ekf2/params_sideslip.yaml

@@ -6,8 +6,8 @@ parameters:
       description:
         short: Enable synthetic sideslip fusion
         long: 'For reliable wind estimation both sideslip and airspeed fusion (see
-          EKF2_ARSP_THR) should be enabled. Only applies to fixed-wing vehicles (or
-          VTOLs in fixed-wing mode). Note: side slip fusion is currently not supported
+          EKF2_ARSP_THR) should be enabled. Only applies to vehicles in fixed-wing mode
+          or with airspeed fusion active. Note: side slip fusion is currently not supported
           for tailsitters.'
       type: boolean
       default: 0