[NETFILTER]: ip6table_mangle: reroute when nfmark changes in NF_IP6_LOCAL_OUT

Now that IPv6 supports policy routing we need to reroute in NF_IP6_LOCAL_OUT
when the mark value changes.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>