ipvs: autoload ipvs on genl access

The kernel provides the functionality to automatically load modules
providing genl families. Use this to remove the need for users to
manually load the module.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>