ipvs: clear skb->tstamp in forwarding path

fq qdisc requires tstamp to be cleared in forwarding path

Reported-by: Evgeny B <abt-admin@mail.ru>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=209427
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: 8203e2d8 ("net: clear skb->tstamp in forwarding paths")
Fixes: fb420d5d ("tcp/fq: move back to CLOCK_MONOTONIC")
Fixes: 80b14dee

 ("net: Add a new socket option for a future transmit time.")
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Reviewed-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>