net: clear skb->tstamp in bridge forwarding path

Matteo reported forwarding issues inside the linux bridge,
if the enslaved interfaces use the fq qdisc.

Similar to commit 8203e2d8 ("net: clear skb->tstamp in
forwarding paths"), we need to clear the tstamp field in
the bridge forwarding path.

Fixes: 80b14dee ("net: Add a new socket option for a future transmit time.")
Fixes: fb420d5d ("tcp/fq: move back to CLOCK_MONOTONIC")
Reported-and-tested-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>