ethtool: pse-pd: fix null-deref on genl_info in dump

ethnl_default_dump_one() passes NULL as info.

It's correct not to set extack during dump, as we should just
silently skip interfaces which can't provide the information.

Reported-by: syzbot+81c4b4bbba6eea2cfcae@syzkaller.appspotmail.com
Fixes: 18ff0bcd ("ethtool: add interface to interact with Ethernet Power Equipment")
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Reviewed-by: NOleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ethtool/pse-pd.c

@@ -64,7 +64,7 @@ static int pse_prepare_data(const struct ethnl_req_info *req_base,
 	if (ret < 0)
 		return ret;
 
-	ret = pse_get_pse_attributes(dev, info->extack, data);
+	ret = pse_get_pse_attributes(dev, info ? info->extack : NULL, data);
 
 	ethnl_ops_complete(dev);