package/iproute2: fix musl build

Fix the following musl build failure raised since bump to version 5.16.0
in commit 8f54d6d7859c0eabf303a44b26e6fafb1cb50143:

ax25_ntop.c:5:10: fatal error: netax25/ax25.h: No such file or directory
    5 | #include <netax25/ax25.h>
      |          ^~~~~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/455840288bbe13ed585b0e2dc7b20a294dd1eee1

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/iproute2/0001-lib-fix-ax25-h-include-for-musl.patch

@@ -0,0 +1,37 @@
+From 8bced38a941a181f1468fa39541e872e51b6022f Mon Sep 17 00:00:00 2001
+From: Sam James <sam@gentoo.org>
+Date: Thu, 13 Jan 2022 08:14:13 +0000
+Subject: [PATCH] lib: fix ax25.h include for musl
+
+ax25.h isn't guaranteed to be avilable in netax25/*;
+it's dependent on our choice of libc (it's not available
+on musl at least) [0].
+
+Let's use the version from linux-headers.
+
+[0] https://sourceware.org/glibc/wiki/Synchronizing_Headers
+Bug: https://bugs.gentoo.org/831102
+
+Signed-off-by: Sam James <sam@gentoo.org>
+Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
+
+[Retrieved from:
+https://github.com/shemminger/iproute2/commit/8bced38a941a181f1468fa39541e872e51b6022f]
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ lib/ax25_ntop.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/lib/ax25_ntop.c b/lib/ax25_ntop.c
+index cfd0e04b0..3a72a43e9 100644
+--- a/lib/ax25_ntop.c
++++ b/lib/ax25_ntop.c
+@@ -2,7 +2,7 @@
+ 
+ #include <errno.h>
+ #include <sys/socket.h>
+-#include <netax25/ax25.h>
++#include <linux/ax25.h>
+ 
+ #include "utils.h"
+