tools: ynl: wrap recv() + mnl_cb_run2() into a single helper

All callers to mnl_cb_run2() call mnl_socket_recvfrom() right before.
Wrap the two in a helper, take typed arguments (struct ynl_parse_arg),
instead of hoping that all callers remember that parser error handling
requires yarg.

In case of ynl_sock_read_family() we will no longer check for kernel
returning no data, but that would be a kernel bug, not worth complicating
the code to catch this. Calling mnl_cb_run2() on an empty buffer
is legal and results in STOP (1).

Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Link: https://lore.kernel.org/r/20240227223032.1835527-9-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>