core: Don't update a known long name with a short name.

core: Don't update a known long name with a short name.

update_found_devices() could attempt to update a device with new information
containing only a short verstion of the name. If the struct eir_data passed
has a short or NULL name, it will never update a previous name and will
also trigger a "HCI Command: Remote Name Request" if the previous name was
unknown.