tools: ynl: Add C array attribute decoding to ynl

Add support for decoding C arrays from binay blobs in genetlink-legacy
messages.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>