ip: add a #define for older kernels

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/libiproute/iplink.c b/networking/libiproute/iplink.c
index 0d90338..9ced18d 100644
--- a/networking/libiproute/iplink.c
+++ b/networking/libiproute/iplink.c
@@ -15,6 +15,9 @@
 #include "rt_names.h"
 #include "utils.h"
 
+#ifndef IFLA_LINKINFO
+# define IFLA_LINKINFO 18
+#endif
 /* taken from linux/sockios.h */
 #define SIOCSIFNAME	0x8923		/* set interface name */