netfilter: fix userspace header warning

"make headers_check" issued the following warning:

  CHECK   include/linux/netfilter (64 files)
usr/include/linux/netfilter/xt_ipvs.h:19: found __[us]{8,16,32,64} type without #include <linux/types.h>

Fix this by as suggested including linux/types.h.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>