EKF: Add control mode for wind state estimation

EKF/common.h

@@ -220,6 +220,7 @@ union filter_control_status_u {
 		uint8_t mag_dec     : 1; // 6 - true if synthetic magnetic declination measurements are being fused
 		uint8_t in_air      : 1; // 7 - true when the vehicle is airborne
 		uint8_t armed       : 1; // 8 - true when the vehicle motors are armed
+		uint8_t wind        : 1; // 9 - true when wind velocity is being estimated
 	} flags;
 	uint16_t value;
 };

EKF/control.cpp

@@ -145,6 +145,12 @@ void Ekf::controlFusionModes()
 		_control_status.flags.mag_dec = false;
 	}
 
+	// Placeholder for control of wind velocity states estimation
+	// TODO add methods for true airspeed and/or sidelsip fusion or some type of drag force measurement
+	if (false) {
+		_control_status.flags.wind = false;
+	}
+
 }
 
 void Ekf::calculateVehicleStatus()