tools/net/ynl: Implement nlattr array-nest decoding in ynl

Add support for the 'array-nest' attribute type that is used by several
netlink-raw families.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230825122756.7603-9-donald.hunter@gmail.com


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