Log analyzer motor balance calculation false error.

#### Issue details
_Please describe the problem, or desired feature_
LogAnalyzer gets 7 output channels to calculate motor balance, it should get 6 channels for the hexacopter.

#### Version
_What version was the issue encountered with_

#### Platform
[ ] All
[ ] AntennaTracker
[ X ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
_What type of airframe (flying wing, glider, hex, Y6, octa etc)_
Hexa

#### Hardware type
_What autopilot hardware was used? (pixhawk, pixracer, PX4FMU etc)_
Pixhawk clone (2.4.6)

#### Logs
_Please provide a link to any relevant logs that show the issue_
Log File C:\Users\mert_\Documents\Mission Planner\logs\HEXAROTOR\1\00000016.log
Size (kb) 12720.5966796875
No of lines 163974
Duration 0:07:49
Vehicletype ArduCopter
Firmware Version V3.5.2
Firmware Hash 4322ffda
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = NA -
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (143.62%)
Max mag field length (1034.96) > recommended (550.00)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = NA -
Test: Motor Balance = FAIL - Motor channel averages = [192, 197, 194, 195, 193, 197, 1131]
Average motor output = 328
Difference between min and max motor averages = 939
Test: Parameters = GOOD -
Test: PM = NA -
Test: Pitch/Roll = NA -
Test: Thrust = NA -
Test: VCC = GOOD -

Start with the Mission Planner LogAnalyzer motor-balance calculation and reproduce the report using the supplied HEXAROTOR log details. Check why a hexacopter produces seven motor channel averages instead of six; done means the analyzer no longer reports the extra channel or a false motor-balance error for this case.

Written by the indexing model from the issue text.