nat: Fix next feature for ED with multiple workers

nat: Fix next feature for ED with multiple workers

Multiple (> 1) workers leads to handoff node being enabled.
This node pops next feature index to nat.arc_next to make sure
that packet will be pushed to the next feature in the arc.

But node nat44-ed-in2out-output also pops next feature and changes
arc_next. So actual next feature will be skipped in that case.

It leads to all nat44-ed-in2out packets being dropped if we have
multiple workers (handoff node enabled).

To resolve this a new node was added (nat-pre-in2out-output) to fill
arc_next in single worker case and multiple worker case is already
handled by handoff node.

Type: fix
Signed-off-by: Vladimir Isaev <visaev@netgate.com>
Change-Id: I9dfba68f00164d2d5ab867224871811bef4411ed