TCP stack relies on the fact that a freshly allocated skb
has skb->cb[] and skb_shinfo(skb)->tx_flags cleared.
When recycling tx skb, we must ensure these fields are cleared.
Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Soheil Hassas Yeganeh <soheil@google.com> Cc: Willem de Bruijn <willemb@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>