ethtool: always write dev in ethnl_parse_header_dev_get

Commit 0976b888 ("ethtool: fix null-ptr-deref on ref tracker")
made the write to req_info.dev conditional, but as Eric points out
in a different follow up the structure is often allocated on the
stack and not kzalloc()'d so seems safer to always write the dev,
in case it's garbage on input.
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Reviewed-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ethtool/netlink.c

@@ -141,10 +141,9 @@ int ethnl_parse_header_dev_get(struct ethnl_req_info *req_info,
 		return -EINVAL;
 	}
 
-	if (dev) {
 	req_info->dev = dev;
+	if (dev)
 		netdev_tracker_alloc(dev, &req_info->dev_tracker, GFP_KERNEL);
-	}
 	req_info->flags = flags;
 	return 0;
 }