RT_CFG_Update_End_Marker_2: Update end marker position
RT_CFG_Test: 159, 20 (0x9F1420 + unit ID) (0x7D4)
Bytes 0-3: End Marker Latitude (degrees)
Bytes 4-7: End Marker Longitude (degrees)
Latitude resolution is degrees * 1e-7.
Longitude resolution is degrees * 1e-7.