evaluate: error reporting for missing statements in set/map declaration

evaluate: error reporting for missing statements in set/map declaration

Assuming this map:

        map y {
                type ipv4_addr : verdict
        }

This patch slightly improves error reporting to refer to the missing
'counter' statement in the map declaration.

 # nft 'add element x y { 1.2.3.4 counter packets 1 bytes 1 : accept, * counter : drop }'
 Error: missing statement in map declaration
 add element x y { 1.2.3.4 counter packets 10 bytes 640 : accept, * counter : drop }
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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