RFR: 8229872: (fs) Increase buffer size used with getmntent

[Florian Weimer]

* Vladimir Kempik:

> Maybe it can  be done it this way:
>
> in jni’s Java_sun_nio_fs_LinuxNativeDispatcher_setmntent0
>
>  go thru file line by line ( with getline) and find longest line, then rewind to file begin.

Interesting idea.  It still has a small race condition.  But it might be
the best compromise between amount of changes required and gains in
robustness.

Thanks,
Florian