Account for delayed-ACKs in H-TCP.

Delayed-ACKs cause H-TCP to be less aggressive than its design calls
for. It is especially true when the receiver is a Linux machine where
the average delayed ack is over 3 packets with values of 7 not unheard
of.
Signed-off-By: Baruch Even <baruch@ev-en.org>
Signed-off-by: David S. Miller <davem@davemloft.net>