[NETFILTER]: x_tables: add missing ip6t_modulename aliases

The patch will add MODULE_ALIAS("ip6t_<modulename>") where missing,
otherwise you will get

	ip6tables: No chain/target/match by that name

when xt_<modulename> is not already loaded.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>