iproute2: Fix netns check during configure

Check would fail with compilers using -Werror since _GNU_SOURCE is
needed for this function.

(From OE-Core rev: f820e177f9d1d1f1c3c9411003e44d04961e1ba4)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-connectivity/iproute2/iproute2/0001-configure-Define-_GNU_SOURCE-when-checking-for-setns.patch

@@ -0,0 +1,28 @@
+From dc837a6b4c2cad7f31cddfe56cd652e26baadc02 Mon Sep 17 00:00:00 2001
+From: Khem Raj <raj.khem@gmail.com>
+Date: Wed, 10 Aug 2022 22:31:03 -0700
+Subject: [PATCH] configure: Define _GNU_SOURCE when checking for setns
+
+glibc defines this function only as gnu extention
+
+Upstream-Status: Submitted [https://lore.kernel.org/netdev/20220811053440.778649-1-raj.khem@gmail.com/T/#u]
+Signed-off-by: Khem Raj <raj.khem@gmail.com>
+---
+ configure | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/configure b/configure
+index 440facb..c02753b 100755
+--- a/configure
++++ b/configure
+@@ -191,6 +191,7 @@ check_ipt_lib_dir()
+ check_setns()
+ {
+     cat >$TMPDIR/setnstest.c <<EOF
++#define _GNU_SOURCE
+ #include <sched.h>
+ int main(int argc, char **argv)
+ {
+-- 
+2.37.1
+

meta/recipes-connectivity/iproute2/iproute2_5.19.0.bb

@@ -3,6 +3,7 @@ require iproute2.inc
 SRC_URI = "${KERNELORG_MIRROR}/linux/utils/net/${BPN}/${BP}.tar.xz \
            file://0001-libc-compat.h-add-musl-workaround.patch \
            file://0001-ip-ipstats.c-add-an-include-where-MIN-is-defined.patch \
+           file://0001-configure-Define-_GNU_SOURCE-when-checking-for-setns.patch \
            "
 
 SRC_URI[sha256sum] = "26b7a34d6a7fd2f7a42e2b39c5a90cb61bac522d1096067ffeb195e5693d7791"