issues with StructOf

- depending whether client or server side, handling of optional is different
- fix issues when struct is used as keyworded command arguments

Change-Id: I72b347b1a96ee3bce1f67dace4862c313c12c7a9
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30972
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/params.py

@@ -492,8 +492,6 @@ class Command(Accessible):
         # pylint: disable=unnecessary-dunder-call
         func = self.__get__(module_obj)
         if self.argument:
-            # validate
-            argument = self.argument(argument)
             if isinstance(self.argument, TupleOf):
                 res = func(*argument)
             elif isinstance(self.argument, StructOf):