netfilter: add include guard to xt_connlabel.h

Add a header include guard just in case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/xt_connlabel.h

 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+
+#ifndef _UAPI_XT_CONNLABEL_H
+#define _UAPI_XT_CONNLABEL_H
+
 #include <linux/types.h>
 
 #define XT_CONNLABEL_MAXBIT 127
@@ -11,3 +15,5 @@ struct xt_connlabel_mtinfo {
 	__u16 bit;
 	__u16 options;
 };
+
+#endif /* _UAPI_XT_CONNLABEL_H */