packet lib: For convenience, make packet into a sequence type

Protocols can mow be accesed as packet[n].

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

ryu/lib/packet/packet.py

@@ -95,3 +95,15 @@ class Packet(object):
 
     def __iter__(self):
         return self
+
+    def __getitem__(self, idx):
+        return self.protocols[idx]
+
+    def __setitem__(self, idx, item):
+        self.protocols[idx] = item
+
+    def __delitem__(self, idx):
+        del self.protocols[idx]
+
+    def __len__(self):
+        return len(self.protocols)