xdrgen: XDR width for optional_data type

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

tools/net/sunrpc/xdrgen/xdr_ast.py

@@ -245,9 +245,19 @@ class _XdrOptionalData(_XdrDeclaration):
     spec: _XdrTypeSpecifier
     template: str = "optional_data"
 
+    def max_width(self) -> int:
+        """Return width of type in XDR_UNITS"""
+        return 1
+
+    def symbolic_width(self) -> List:
+        """Return list containing XDR width of type's components"""
+        return ["XDR_bool"]
+
     def __post_init__(self):
         structs.add(self.name)
         pass_by_reference.add(self.name)
+        max_widths[self.name] = self.max_width()
+        symbolic_widths[self.name] = self.symbolic_width()
 
 
 @dataclass