pyln.proto: fix handling of subtypes in TLVs.

This was revealed by using lnprototest on channel_types.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

contrib/pyln-proto/pyln/proto/message/message.py

@@ -305,8 +305,8 @@ def write(self, io_out: BufferedIOBase, v: Dict[str, Any], otherfields: Dict[str
                     raise ValueError("Missing field {} {}".format(f.name, otherfields))
                 val = None
 
-            if self.name in otherfields:
-                otherfields = otherfields[self.name]
+            if type(f.fieldtype) is SubtypeType:
+                otherfields = otherfields[f.name]
             f.fieldtype.write(io_out, val, otherfields)
 
     def read(self, io_in: BufferedIOBase, otherfields: Dict[str, Any]) -> Optional[Dict[str, Any]]:
@@ -554,7 +554,7 @@ def get_value(tup):
 
         for typenum, writefunc, val in ordered:
             buf = BytesIO()
-            writefunc(cast(BufferedIOBase, buf), val, otherfields)
+            writefunc(cast(BufferedIOBase, buf), val, val)
             BigSizeType.write(io_out, typenum)
             BigSizeType.write(io_out, len(buf.getvalue()))
             io_out.write(buf.getvalue())