[TCP]: Don't use highmem in tcp hash size calculation.

This patch removes consideration of high memory when determining TCP
hash table sizes.  Taking into account high memory results in tcp_mem
values that are too large.

Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>