tools/net/ynl: Encode default values for binary blobs

Add support for defaulting binary byte arrays to all zeros as well as
defaulting scalar values to 0 when encoding input parameters.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240129223458.52046-7-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>