update config.h.in file to enable loopback mount detection

Commit fbabd5c44c23 added loopback mount detection.  However, we
failed to update the config.h file, so the code wasn't actually
enabled.  Fix this oversight.

Addresses-Debian-Bug: #497984

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
1 file changed