netfilter: nf_fwd_netdev: clear timestamp in forwarding path

[ Upstream commit c77761c8a59405cb7aa44188b30fffe13fbdd02d ]

Similar to 7980d2eabde8 ("ipvs: clear skb->tstamp in forwarding path").
fq qdisc requires tstamp to be cleared in forwarding path.

Fixes: 8203e2d844d3 ("net: clear skb->tstamp in forwarding paths")
Fixes: fb420d5d91c1 ("tcp/fq: move back to CLOCK_MONOTONIC")
Fixes: 80b14dee ("net: Add a new socket option for a future transmit time.")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>