packet lib: set protocol_name in each protocol

With this, it's easy to know the protocol name.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

ryu/lib/packet/packet_base.py

@@ -28,6 +28,7 @@ class PacketBase(object):
     def __init__(self):
         super(PacketBase, self).__init__()
         self.length = 0
+        self.protocol_name = self.__class__.__name__
 
     @classmethod
     def parser(cls):