netfilter.h needs rcuupdate.h for RCU locking functions

This was exposed by Al's recent header file dependency reduction
patches..

Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

include/linux/netfilter.h

@@ -11,6 +11,7 @@
 #include <linux/list.h>
 #endif
 #include <linux/compiler.h>
+#include <linux/rcupdate.h>
 
 /* Responses from hook functions. */
 #define NF_DROP 0