[NETFILTER]: Change tunables to __read_mostly

Change some netfilter tunables to __read_mostly.  Also fixed some
incorrect file reference comments while I was in there.

(this will be my last __read_mostly patch unless someone points out
something else that needs it)

Signed-off-by: Brian Haley <brian.haley@hp.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>