src: allow to map key to nfqueue number

src: allow to map key to nfqueue number

Allow to specify a numeric queue id as part of a map.
The parser side is easy, but the reverse direction (listing) is not.

'queue' is a statement, it doesn't have an expression.

Add a generic 'queue_type' datatype as a shim to the real basetype with
constant expressions, this is used only for udata build/parse, it stores
the "key" (the parser token, here "queue") as udata in kernel and can
then restore the original key.

Add a dumpfile to validate parser & output.

JSON support is missing because JSON allow typeof only since quite
recently.

Joint work with Pablo.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1455
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>