netlabel: fix build problems when CONFIG_IPV6=n

My last patch to solve a problem where the static/fallback labels were
not fully displayed resulted in build problems when IPv6 was disabled.
This patch resolves the IPv6 build problems; sorry for the screw-up.

Please queue for -stable or simply merge with the previous patch.

Reported-by: Kbuild Test Robot <fengguang.wu@intel.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>