src: parser_json: fix format string bugs

src: parser_json: fix format string bugs

After adding fmt attribute annotation:
warning: format not a string literal and no format arguments [-Wformat-security]
  131 |         erec_queue(error(&loc, err->text), ctx->msgs);
In function 'json_events_cb':
warning: format '%lu' expects argument of type 'long unsigned int', but argument 3 has type '__u32' {aka 'unsigned int'} [-Wformat=]

Fix that up too.

Fixes: 586ad210368b ("libnftables: Implement JSON parser")
Signed-off-by: Florian Westphal <fw@strlen.de>