netlink: provide a fallback definition of NETLINK_SOCK_DIAG

Add a fallback definition of NETLINK_SOCK_DIAG to netlink.h
instead of adding these fallback definitions to every file.

* netlink.h: Provide a fallback definition of NETLINK_SOCK_DIAG.
* socketutils.c: Include "netlink.h" instead of <linux/netlink.h>,
remove fallback definition of NETLINK_SOCK_DIAG.

netlink.h

@@ -32,6 +32,10 @@
 #include <sys/socket.h>
 #include <linux/netlink.h>
 
+#ifndef NETLINK_SOCK_DIAG
+# define NETLINK_SOCK_DIAG 4
+#endif
+
 #undef NLMSG_HDRLEN
 #define NLMSG_HDRLEN ((unsigned int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
 

socketutils.c

@@ -31,7 +31,7 @@
 #include <netinet/in.h>
 #include <sys/socket.h>
 #include <arpa/inet.h>
-#include <linux/netlink.h>
+#include "netlink.h"
 #include <linux/sock_diag.h>
 #include <linux/inet_diag.h>
 #include <linux/unix_diag.h>
@@ -46,10 +46,6 @@
 # define UNIX_PATH_MAX sizeof(((struct sockaddr_un *) 0)->sun_path)
 #endif
 
-#ifndef NETLINK_SOCK_DIAG
-# define NETLINK_SOCK_DIAG 4
-#endif
-
 typedef struct {
 	unsigned long inode;
 	char *details;