If the timeout of an autofs mount is set to zero then umounts are disabled.
 This works fine, however the kernel module checks the expire timeout and
goes no further if it is zero.  This is not the right thing to do at
shutdown as the module is passed an option to expire mounts regardless of
their timeout setting.

This patch allows autofs to honor the force expire option.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>