package/ethtool: add patch to fix build failures

Add a patch from the kernel netdev mailing list [1] that solves
autobuilder failures.

Fixes:
http://autobuild.buildroot.net/results/394e846bb48a0cc8564ebc3e8d1179ccd1f1560d/

[1] bb60cbfe99.1590707335.git.mkubecek@suse.cz/

Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/ethtool/0001-netlink-fix-build-warnings.patch

@@ -0,0 +1,52 @@
+From 93b2d0ef0c2be825e56d1f810fbbfba4800fa831 Mon Sep 17 00:00:00 2001
+From: Michal Kubecek <mkubecek@suse.cz>
+Date: Fri, 29 May 2020 01:21:12 +0200
+Subject: [PATCH] netlink: fix build warnings
+
+Depending on compiler version and options, some of these warnings may
+result in build failure.
+
+- gcc 4.8 wants __KERNEL_DIV_ROUND_UP defined before including ethtool.h
+- avoid pointer arithmetic on void *
+
+Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
+
+[Patch was taken from the linux netdev mailinglist and will be applied in the
+upcoming ethtool release 5.8]
+Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
+---
+ netlink/desc-ethtool.c | 2 +-
+ netlink/parser.c       | 2 +-
+ 2 files changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/netlink/desc-ethtool.c b/netlink/desc-ethtool.c
+index 76c6f13..423479d 100644
+--- a/netlink/desc-ethtool.c
++++ b/netlink/desc-ethtool.c
+@@ -4,9 +4,9 @@
+  * Descriptions of ethtool netlink messages and attributes for pretty print.
+  */
+ 
++#include "../internal.h"
+ #include <linux/ethtool_netlink.h>
+ 
+-#include "../internal.h"
+ #include "prettymsg.h"
+ 
+ static const struct pretty_nla_desc __header_desc[] = {
+diff --git a/netlink/parser.c b/netlink/parser.c
+index fff23f2..d790abe 100644
+--- a/netlink/parser.c
++++ b/netlink/parser.c
+@@ -1016,7 +1016,7 @@ int nl_parser(struct nl_context *nlctx, const struct param_parser *params,
+ 			buff = tmp_buff_find(buffs, parser->group);
+ 		msgbuff = buff ? &buff->msgbuff : &nlsk->msgbuff;
+ 
+-		param_dest = dest ? (dest + parser->dest_offset) : NULL;
++		param_dest = dest ? ((char *)dest + parser->dest_offset) : NULL;
+ 		ret = parser->handler(nlctx, parser->type, parser->handler_data,
+ 				      msgbuff, param_dest);
+ 		if (ret < 0)
+-- 
+2.20.1
+