[NETLABEL]: Don't produce unused variables when IPv6 is off.

Some code declares variables on the stack, but uses them
under #ifdef CONFIG_IPV6, so thay become unused when ipv6
is off. Fortunately, they are used in a switch's case
branches, so the fix is rather simple.

Is it OK from coding style POV to add braces inside "cases",
or should I better avoid such style and rework the patch?

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>