fix pcap.Reader.next() compatibility Python 2-3 (#473)

Author: shadchin

dpkt/pcap.py

@@ -312,6 +312,7 @@ def readpkts(self):
 
     def __next__(self):
         return next(self.__iter)
+    next = __next__  # Python 2 compat
 
     def dispatch(self, cnt, callback, *args):
         """Collect and process packets with a user callback.

dpkt/pcapng.py

@@ -589,8 +589,9 @@ def setfilter(self, value, optimize=1):
     def readpkts(self):
         return list(self)
 
-    def next(self):
+    def __next__(self):
         return next(self.__iter)
+    next = __next__  # Python 2 compat
 
     def dispatch(self, cnt, callback, *args):
         """Collect and process packets with a user callback.