[TCP]: NAGLE_PUSH seems to be a wrong way around

The comment in tcp_nagle_test suggests that. This bug is very
very old, even 2.4.0 seems to have it.

Signed-off-by: Ilpo Jrvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>