netfilter: ip6table_mangle: don't reroute in LOCAL_IN

Rerouting should only happen in LOCAL_OUT, in INPUT its useless
since the packet has already chosen its final destination.

Noticed by Alexey Dobriyan <adobriyan@gmail.com>.

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