of1.3: parser should return msg, not implicit None

And OFPSetConfig should have serializer, not parser Because the message
is sent by controller to OF switch.

Cc: nitish nagesh <nagesh.nitish@gmail.com>
Cc: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>