[IPV6]: Cleanup the addconf_sysctl_register

This only includes fixing the space-indented lines and
removing one unneeded else after the goto.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>