devlink: fix libc and kernel headers collision

Since commit 2f1242efe9 ("devlink: Add devlink health show command") we
use the sys/sysinfo.h header for the sysinfo(2) system call. But since
iproute2 carries a local version of the kernel struct sysinfo, this
causes a collision with libc that do not rely on kernel defined sysinfo
like musl libc:

In file included from devlink.c:25:0:
.../sysroot/usr/include/sys/sysinfo.h:10:8: error: redefinition of 'struct sysinfo'
 struct sysinfo {
        ^~~~~~~
In file included from ../include/uapi/linux/kernel.h:5:0,
                 from ../include/uapi/linux/netlink.h:5,
                 from ../include/uapi/linux/genetlink.h:6,
                 from devlink.c:21:
../include/uapi/linux/sysinfo.h:8:8: note: originally defined here
 struct sysinfo {
        ^~~~~~~

Move the sys/sysinfo.h userspace header before kernel headers, and
suppress the indirect include of linux/sysinfo.h.

Cc: Aya Levin <ayal@mellanox.com>
Cc: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

devlink/devlink.c

@@ -19,11 +19,12 @@
 #include <limits.h>
 #include <errno.h>
 #include <inttypes.h>
+#include <sys/sysinfo.h>
+#define _LINUX_SYSINFO_H /* avoid collision with musl header */
 #include <linux/genetlink.h>
 #include <linux/devlink.h>
 #include <libmnl/libmnl.h>
 #include <netinet/ether.h>
-#include <sys/sysinfo.h>
 #include <sys/queue.h>
 
 #include "SNAPSHOT.h"