RC_Channel: support up to 12 aux channels on PX4

this allows RC13 and RC14 to work correctly as aux outputs on Pixhawk
DataFlash: support logging up to 14 RC input channels
AP_NavEKF : Reduce GPS position innovation consistency fail threshold

This patch reduces the maximum acceptable GPS jump from approximately 16 to 8 metres
This will provide copters with more protection for close in loiter situations
AP_NavEKF : Reduce Magnetometer innovation consistency check threshold