ekf2: Enable use of flow sensors not fitted with gyros (#9703)

* ecl: Update to version allowing use of flow sensors without gyros

* msg: Update description for optical_flow

Adds advice for publishing gyro rate integral message when no rate gyro is fitted.

msg/optical_flow.msg

@@ -4,9 +4,9 @@
 uint8 sensor_id			# id of the sensor emitting the flow value
 float32 pixel_flow_x_integral	# accumulated optical flow in radians where a positive value is produced by a RH rotation about the X body axis
 float32 pixel_flow_y_integral	# accumulated optical flow in radians where a positive value is produced by a RH rotation about the Y body axis
-float32 gyro_x_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the X body axis
-float32 gyro_y_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the Y body axis
-float32 gyro_z_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the Z body axis
+float32 gyro_x_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the X body axis. Set to NaN if flow sensor does not have 3-axis gyro data.
+float32 gyro_y_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the Y body axis. Set to NaN if flow sensor does not have 3-axis gyro data.
+float32 gyro_z_rate_integral	# accumulated gyro value in radians where a positive value is produced by a RH rotation about the Z body axis. Set to NaN if flow sensor does not have 3-axis gyro data.
 float32 ground_distance_m	# Altitude / distance to ground in meters
 uint32 integration_timespan	# accumulation timespan in microseconds
 uint32 time_since_last_sonar_update	# time since last sonar update in microseconds

src/lib/ecl

@@ -1 +1 @@
-Subproject commit 1a1106878d6ab1cc48565bef9b25b07d626c5d0b
+Subproject commit 1cba257bac94ffe7c9b48fb9ff9de73c582d68d8