vboxsf file timestamp not set properly

[Norbert Novotny]

Setting file modification timestamp on a file seated in shared folder does not work properly.

The case description:

$ df -h .
Filesystem      Size  Used Avail Use% Mounted on
Shared          932G  317G  616G  34% /media/sf_Shared
$ mount -l | grep Shared
Shared on /media/sf_Shared type vboxsf (rw,nodev,relatime)
$ touch -md "1970-01-01 00:00:00"   test
$ ls -l test
-rwxrwx--- 1 root vboxsf 0 '''Jul 22  2554''' test

Doing the same on a native fs does work as expected.