iproute2: add missing limits.h includes

This patch has been submitted upstream to fix an error reported by a few
users. One instance seen using gcc 10.2.0, binutils 2.35.1 and musl 1.1.24:

bpf_glue.c: In function 'get_libbpf_version':
bpf_glue.c:46:11: error: 'PATH_MAX' undeclared (first use in this function);
did you mean 'AF_MAX'?
   46 |  char buf[PATH_MAX], *s;
      |           ^~~~~~~~
      |           AF_MAX

Reported-by: Rui Salvaterra <rsalvaterra@gmail.com>
Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
(cherry picked from commit 10ffefe602)

package/network/utils/iproute2/patches/185-libbpf-add-limits-h.patch

@@ -0,0 +1,45 @@
+From c77310119f9a5f99221dd967c5eb0c7a26094b41 Mon Sep 17 00:00:00 2001
+From: Tony Ambardar <Tony.Ambardar@gmail.com>
+Date: Wed, 3 Mar 2021 10:29:24 -0800
+Subject: [PATCH] lib/bpf: add missing limits.h includes
+
+Several functions in bpf_glue.c and bpf_libbpf.c rely on PATH_MAX, which is
+normally included from <limits.h> in other iproute2 source files.
+
+It fixes errors seen using gcc 10.2.0, binutils 2.35.1 and musl 1.1.24:
+
+bpf_glue.c: In function 'get_libbpf_version':
+bpf_glue.c:46:11: error: 'PATH_MAX' undeclared (first use in this function);
+did you mean 'AF_MAX'?
+   46 |  char buf[PATH_MAX], *s;
+      |           ^~~~~~~~
+      |           AF_MAX
+
+Reported-by: Rui Salvaterra <rsalvaterra@gmail.com>
+Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
+---
+ lib/bpf_glue.c   | 2 ++
+ lib/bpf_libbpf.c | 1 +
+ 2 files changed, 3 insertions(+)
+
+--- a/lib/bpf_glue.c
++++ b/lib/bpf_glue.c
+@@ -4,6 +4,8 @@
+  * Authors:	Hangbin Liu <haliu@redhat.com>
+  *
+  */
++#include <limits.h>
++
+ #include "bpf_util.h"
+ #ifdef HAVE_LIBBPF
+ #include <bpf/bpf.h>
+--- a/lib/bpf_libbpf.c
++++ b/lib/bpf_libbpf.c
+@@ -13,6 +13,7 @@
+ #include <stdint.h>
+ #include <errno.h>
+ #include <fcntl.h>
++#include <limits.h>
+ 
+ #include <libelf.h>
+ #include <gelf.h>