Fix reversed logic.

This error was causing stat vol = no to be put in AFP
shares by default.  The netatalk default for this setting is yes.

I believe this is responsible for a wide range of breakage in netatalk.
This restores the correct behavior.  If you check the box labeled no stat
(which is only visible under advanced) then it will put stat vol = no in
for that share.

Otherwise, the default value for a share created with FreeNAS will be to
use the netatalk value for this field, which is stat vol = yes.