Revert "tools/net/ynl: improve async notification handling"

This reverts commit 1bf70e6c.

This modification to check_ntf() is being reverted so that its behaviour
remains equivalent to ynl_ntf_check() in the C YNL. Instead a new
poll_ntf() will be added in a separate patch.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20241113090843.72917-2-donald.hunter@gmail.com


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