netfilter: nf_flow_table: fix offloading connections with SNAT+DNAT

Pass all NAT types to the flow offload struct, otherwise parts of the
address/port pair do not get translated properly, causing connection
stalls

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>