evaluate: properly set datatype of map expression

evaluate: properly set datatype of map expression

The datatype of the map expression is the datatype of the mappings.

# nft add map filter test { type ipv4_addr : inet_service; }
# nft filter output mark set ip daddr map @test

Before:

<cmdline>:1:24-41: Error: datatype mismatch: expected packet mark, expression has type IPv4 address
filter output mark set ip daddr map @test
              ~~~~~~~~~^^^^^^^^^^^^^^^^^^

After:

<cmdline>:1:24-41: Error: datatype mismatch: expected packet mark, expression has type internet network service
filter output mark set ip daddr map @test
              ~~~~~~~~~^^^^^^^^^^^^^^^^^^

Signed-off-by: Patrick McHardy <kaber@trash.net>