tools: ynl-gen: always construct struct ynl_req_state

struct ynl_req_state carries reply-related info from generated code
into generic YNL code. While we don't need reply info to execute
a request without a reply, we still need to pass in the struct, because
it's also where we get the pointer to struct ynl_sock from. Passing NULL
results in crashes if kernel returns an error or an unexpected reply.

Fixes: dc0956c ("tools: ynl-gen: move the response reading logic into YNL")
Link: https://lore.kernel.org/r/20231126225858.2144136-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>