evaluate: Perform set evaluation on implicitly declared (anonymous) sets

evaluate: Perform set evaluation on implicitly declared (anonymous) sets

If a set is implicitly declared, set_evaluate() is not called as a
result of cmd_evaluate_add(), because we're adding in fact something
else (e.g. a rule). Expression-wise, evaluation still happens as the
implicit set expression is eventually found in the tree and handled
by expr_evaluate_set(), but context-wise evaluation (set_evaluate())
is skipped, and this might be relevant instead.

This is visible in the reported case of an anonymous set including
concatenated ranges:

  # nft add rule t c ip saddr . tcp dport { 192.0.2.1 . 20-30 } accept
  BUG: invalid range expression type concat
  nft: expression.c:1160: range_expr_value_low: Assertion `0' failed.
  Aborted

because we reach do_add_set() without properly evaluated flags and
set description, and eventually end up in expr_to_intervals(), which
can't handle that expression.

Explicitly call set_evaluate() as we add anonymous sets into the
context, and instruct the same function to:
- skip expression-wise set evaluation if the set is anonymous, as
  that happens later anyway as part of the general tree evaluation
- skip the insertion in the set cache, as it makes no sense to have
  sets that shouldn't be referenced there

For object maps, the allocation of the expression for set->data is
already handled by set_evaluate(), so we can now drop that from
stmt_evaluate_objref_map().

v2:
 - skip insertion of set in cache (Pablo Neira Ayuso)
 - drop double allocation of expression (and leak of the first
   one) for object maps (Pablo Neira Ayuso)

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Reported-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>