src: permit use of constant values in set lookup keys

src: permit use of constant values in set lookup keys

commit b422b07ab2f96436001f33dfdfd937238033c799 upstream.

Something like:

Given: set s { type ipv4_addr . ipv4_addr . inet_service .. } something
like
   add rule ip saddr . 1.2.3.4 . 80 @s goto c1

fails with: "Error: Can't parse symbolic invalid expressions".

This fails because the relational expression first evaluates
the left hand side, so when concat evaluation sees '1.2.3.4'
no key context is available.

Check if the RHS is a set reference, and, if so, evaluate
the right hand side.

This sets a pointer to the set key in the evaluation context
structure which then makes the concat evaluation step parse
1.2.3.4 and 80 as ipv4 address and 16bit port number.

On delinearization, extend relop postprocessing to
copy the datatype from the rhs (set reference, has
proper datatype according to set->key) to the lhs (concat
expression).

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