use "glibc errno" trick not only for ash, but for entire busybox
(add/remove: 1/1 grow/shrink: 37/37 up/down: 139/-228)        Total: -89 bytes

diff --git a/networking/libiproute/libnetlink.c b/networking/libiproute/libnetlink.c
index 5307cec..0f60409 100644
--- a/networking/libiproute/libnetlink.c
+++ b/networking/libiproute/libnetlink.c
@@ -11,16 +11,10 @@
  *
  */
 
-#include "libbb.h"
 #include <sys/socket.h>
-
-#include <errno.h>
-#include <string.h>
-#include <time.h>
-#include <unistd.h>
-
 #include <sys/uio.h>
 
+#include "libbb.h"
 #include "libnetlink.h"
 
 void rtnl_close(struct rtnl_handle *rth)