linux: enable CONFIG_FHANDLE

Udev has race conditions without it enabled, see
https://www.mail-archive.com/systemd-devel@lists.freedesktop.org/msg16660.html
for more details.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Merge pull request #41 from koenkooi/udev-fix

linux: enable CONFIG_FHANDLE