tools: ynl: don't use genlmsghdr in classic netlink

tools: ynl: don't use genlmsghdr in classic netlink

Make sure the codegen calls the right YNL lib helper to start
the request based on family type. Classic netlink request must
not include the genl header.

Conversely don't expect genl headers in the responses.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250410014658.782120-10-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>