evaluate: missing object maps handling in list and flush commands

evaluate: missing object maps handling in list and flush commands

NFT_SET_OBJECT tells there is an object map.

 # nft list ruleset
 table inet filter {
        map countermap {
                type ipv4_addr : counter
        }
 }

The following command fails:

 # nft flush set inet filter countermap

This patch checks for NFT_SET_OBJECT from new set_is_literal() and
map_is_literal() functions. This patch also adds tests for this.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>