sharkd: check if JSON value is string or primitive (true/false/null/number).

sharkd: check if JSON value is string or primitive (true/false/null/number).

Add extra check for token type, previously it was possible to pass for example:
{"columns":["one","two","three"]}. Such format is not supported.

Change-Id: I6ac2e3ca9eba868cd72ed886ad40745ebbc43d73
Reviewed-on: https://code.wireshark.org/review/23834
Petri-Dish: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>