AP_Arming: arm_check: always check for estop

[IamPete1]

If someone setups the arm - emergency stop aux function and you arm another way its very easy to get confused as to why the motors don't work.

In the pre-arm checks we don't check for estop if the arm-estop function is assigned because it would always fail.

ardupilot/libraries/AP_Arming/AP_Arming.cpp

Lines 1661 to 1669 in ecb7568

	// vehicle is emergency-stopped; if this *appears* to have been done via switch then we do not fail prearms:
	const RC_Channel *chan = rc().find_channel_for_option(RC_Channel::AUX_FUNC::ARM_EMERGENCY_STOP);
	if (chan != nullptr) {
	// an RC channel is configured for arm_emergency_stop option, so estop maybe activated via this switch
	if (chan->get_aux_switch_pos() == RC_Channel::AuxSwitchPos::LOW) {
	// switch is configured and is in estop position, so likely the reason we are estopped, so no prearm failure
	return true; // no prearm failure
	}
	}

In the arm check itself that aux function will no longer be in the e-stop position if it has been used to trigger the arming attempt. If your trying to arm some other way you will see the message.

Classification & Testing (check all that apply and add your own)

• Checked by a human programmer
• Non-functional change
• No-binary change
• Infrastructure change (e.g. unit tests, helper scripts)
• Automated test(s) verify changes (e.g. unit test, autotest)
• Tested manually, description below (e.g. SITL)
• Tested on hardware
• Logs attached
• Logs available on request

Tested in SITL that the arm - emergency stop aux function still works as expected but now we get the arm check if arming using another method.

[peterbarker]

LGTM

[IamPete1]

On the call we realized a nastier problem which this also fixes. If you have arm / estop setup and arm another way you end up with the vehicle armed but with estop on. If you then remember your estop switch and flick it the vehicle comes to life suddenly at whatever throttle position you happened to be at.

[Georacer]

This has been included in 4.7.0-beta4. Thanks!