autotest: fix FenceFloorEnabledLanding test

[andyp1per]

This test had erroneous behaviour, now fixed.

[peterbarker]

Could you explain what this test is supposed to be testing?

The test description is the same as another test in there, so I can't really trust it - the description does look correct for the other test.

The test doesn't seem to make sense as-written; it enters recovery mode, then waits for it to timeout, which should re-trigger the fence action - RTL - but then it fiddles with RC as if that will make a difference.

If I understand what's happening correctly this is actually a pretty serious bug in the fence logic.

When passing, the vehicle enters RTL and the disarm-on-land code within the mode triggers. When failing the vehicle stays in LOITER for what seems an unlimited period below the fence. The vehicle will not disarm in loiter when the landing detector fires as the relevant option bit it not set.

So... what is supposed to happen in this test? An assert_mode or two in here would not go astray!

[peterbarker]

[peterbarker]

LGTM, thanks!