Minor jstest reporting issues

[TehFreek]

hid-tflight4 git03726d87
kernel 5.14.16-201.fc34.x86_64

The module works mostly well, thanks for your work on it. The only issues I'm seeing with it are:

• Axis 8 (9 with throttle_seesaw_extra_axis=1) (labelled "(null)" in jstest) is a duplicate of axis 0, stick X.
• Axes 2 and 3 (3 and 4) are reflections (i.e. -32767 when released, 32767 when pressed) of buttons 6 ("L2", BtnTL) and 7 ("R2", BtnTR) respectively. This isn't a big deal, but it may confuse applications that check both axes and buttons when reassigning bindings.
• Button 13 (BtnThumbL), uh, doesn't seem to exist on my device. Is there a revision of the T.Flight HOTAS 4 that has this button?

[walterschell]

Reproduced. Working in issue/8-extra-axis-and-buttons branch

• - Dupe of stick X axis
• - Extra axis mirroring buttons
• - Extra button in descriptor