netlink: use <linux/export.h> instead of <linux/module.h>

Since (9f00d977 netlink: hide struct module parameter in netlink_kernel_create),
linux/netlink.h includes linux/module.h because of the use of THIS_MODULE.

Use linux/export.h instead, as suggested by Stephen Rothwell, which is
significantly smaller and defines THIS_MODULES.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netlink.h

@@ -153,7 +153,7 @@ struct nlattr {
 
 #include <linux/capability.h>
 #include <linux/skbuff.h>
-#include <linux/module.h>
+#include <linux/export.h>
 #include <net/scm.h>
 
 struct net;