netfilter: xtables: add missing header inclusions for headers_check

Resolve these warnings on `make headers_check`:

usr/include/linux/netfilter/xt_CT.h:7: found __[us]{8,16,32,64} type
without #include <linux/types.h>
...

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/include/linux/netfilter_bridge/ebt_stp.h b/include/linux/netfilter_bridge/ebt_stp.h
index 13a0bd4..1025b9f 100644
--- a/include/linux/netfilter_bridge/ebt_stp.h
+++ b/include/linux/netfilter_bridge/ebt_stp.h
@@ -1,6 +1,8 @@
 #ifndef __LINUX_BRIDGE_EBT_STP_H
 #define __LINUX_BRIDGE_EBT_STP_H
 
+#include <linux/types.h>
+
 #define EBT_STP_TYPE		0x0001
 
 #define EBT_STP_FLAGS		0x0002