tools: ynl-gen: array-nest: support binary array with exact-len

tools: ynl-gen: array-nest: support binary array with exact-len

IPv6 addresses are expressed as binary arrays since we don't have u128.
Since they are not variable length, however, they are relatively
easy to represent as an array of known size.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250429154704.2613851-11-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>