conntrack: T4740: Set correct error msg if enrties not found
conntrack: T4740: Set correct error msg if enrties not found

Set correct error message if conntrack entries not found
If we get XML raw data with len 0 it means there are no entries
in the conntrack table

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x