[NETFILTER]: nfnetlink: fix ifdef in nfnetlink_compat.h

Use __KERNEL__ instead of __KERNEL to make sure the headers are not
usable by the kernel.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter/nfnetlink_compat.h

 #ifndef _NFNETLINK_COMPAT_H
 #define _NFNETLINK_COMPAT_H
-#ifndef __KERNEL
+#ifndef __KERNEL__
 /* Old nfnetlink macros for userspace */
 
 /* nfnetlink groups: Up to 32 maximum */