src: allow use of 'verdict' in typeof definitions

src: allow use of 'verdict' in typeof definitions

'verdict' cannot be used as part of a map typeof-based key definition,
its a datatype and not an expression, e.g.:

  typeof iifname . ip protocol . th dport : verdic

... will fail.

Make the parser convert a 'verdict' symbol to a verdict expression
and allow to store its presence as part of the typeof key definition.

Reported-by: Frank Myhr <fmyhr@fhmtech.com>
Signed-off-by: Florian Westphal <fw@strlen.de>