external mousewheel slow scrolling

[Johan Vos]

Hi Phil,

The fix for JDK-8183399 [1] introduced a new issue: if an external mouse
with a real mousewheel is used for scrolling, the new scrollvalues are a
factor 10 too low.
I created a new bug for this (JDK-8218424) [2] and Jose created a PR to fix
this [3]. I'll review that PR shortly.

Can you also review this PR?

Thanks,

- Johan

[1] https://bugs.openjdk.java.net/browse/JDK-8183399
[2] https://bugs.openjdk.java.net/browse/JDK-8218424
[3] https://github.com/javafxports/openjdk-jfx/pull/371