autocore: cleanup err output

Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>

package/emortal/autocore/files/generic/ethinfo

@@ -2,7 +2,7 @@
 
 for i in $(ip address | grep -E 'eth[0-9]+' | awk -F ': ' '{print $2}' | xargs)
 do
-	device_info="$(ethtool "$i")" || continue
+	device_info="$(ethtool "$i" 2>"/dev/null")" || continue
 
 	if echo -e "$device_info" | grep -Eq 'Link detected.*yes'; then
 		link_stat=1