Error on channels not used

#### Issue details
Error on channels not used. In the flight-data window indicates a message the errors (for example)
CH9 (CH13, CH14 etc.) trim lower than minimum.
These channels are not calibrated and also on the transmitter, Futaba T14SG, not used. In the previous Arducopter firmware, I solved the problem by correcting the values in the parameter list and save the data. After the update to V 3.6.6 appears the problem again. My work around is, to configure all these channels to one sender unit and calibrate them in mission planner. But what will all the other user do in the case of haven’t so much channels on their transmitter?
Please correct these errors in the next stable version with usual values for trim-values grater than the minimum values.

#### Version
ArduCopter V 3.6.6 and previous versions
#### Platform
[ ] All
[ ] AntennaTracker
[ X ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
X-Copter
#### Hardware type
Pixhawk 2.1
#### Logs
non

Start by investigating the Flight Data window's handling of trim-minimum warnings for unused or uncalibrated channels on Copter V3.6.6 with a Pixhawk 2.1. Reproduce the CH9/CH13/CH14 messages using the issue's transmitter configuration and determine the expected behavior for channels that are not used; done means the erroneous warnings no longer appear without requiring calibration of unavailable channels.

Written by the indexing model from the issue text.