tcp: address problems caused by EDT misshaps

tcp: address problems caused by EDT misshaps

When a qdisc setup including pacing FQ is dismantled and recreated,
some TCP packets are sent earlier than instructed by TCP stack.

TCP can be fooled when ACK comes back, because the following
operation can return a negative value.

    tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;

Some paths in TCP stack were not dealing properly with this,
this patch addresses four of them.

Fixes: ab408b6dc744 ("tcp: switch tcp and sch_fq to new earliest departure time model")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>