python: remove use of PyArg_ParseTuple() for callback result

python: remove use of PyArg_ParseTuple() for callback result

The message receive callback handler in the netlink api processes
the result object from the python callback. It used PyArg_ParseTuple()
to get the value, but this does not work as intended (see ref [1]).
Instead check the type and convert it accordingly.

refs:
[1] http://stackoverflow.com/questions/13636711/what-is-the-proper-usage-of-pyarg-parsetuple

Reported-by: Teto <mattator@gmail.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Thomas Graf <tgraf@suug.ch>