common.xml: add MAV_MOUNT_MODE_WPNEXT_OFFSET

to match the command you can give th toe gimbal

Author: peterbarker

message_definitions/v1.0/common.xml

@@ -383,6 +383,9 @@
       <entry value="6" name="MAV_MOUNT_MODE_HOME_LOCATION">
         <description>Gimbal tracks home position</description>
       </entry>
+      <entry value="7" name="MAV_MOUNT_MODE_WPNEXT_OFFSET">
+        <description>Gimbal tracks next waypoint location with offset</description>
+      </entry>
     </enum>
     <enum name="GIMBAL_DEVICE_CAP_FLAGS" bitmask="true">
       <description>Gimbal device (low level) capability flags (bitmap).</description>