evaluate: check that set type is identical before merging

evaluate: check that set type is identical before merging

commit 5335452966c4e5da2f3a5cf617cf431d711b215e upstream.

Reject maps and sets of the same name:
 BUG: invalid range expression type catch-all set element
 nft: src/expression.c:1704: range_expr_value_low: Assertion `0' failed.

After:
Error: Cannot merge set with existing datamap of same name
  set z {
      ^

v2:
Pablo points out that we shouldn't merge datamaps (plain value) and objref
maps either, catch this too and add another test:

nft --check -f invalid_transcation_merge_map_and_objref_map
invalid_transcation_merge_map_and_objref_map:9:13-13: Error: Cannot merge map with incompatible existing map of same name

We should also make sure that both data (for map case) and
set keys are identical, this is added in a followup patch.

Signed-off-by: Florian Westphal <fw@strlen.de>