Python3 compatability for tests

Couple regressions that mostly slipped in with the recent hashing changes.

  https://trac.torproject.org/projects/tor/ticket/27030

stem/client/datatype.py

@@ -349,6 +349,7 @@ class Size(Field):
     self.name = name
     self.size = size
     self.format = pack_format
+    self._hash = None
 
   @staticmethod
   def pop(packed):
@@ -376,6 +377,12 @@ class Size(Field):
 
     return self.unpack(to_unpack), remainder
 
+  def __hash__(self):
+    if self._hash is None:
+      self._hash = stem.util._hash_attr(self, 'name', 'size', 'format')
+
+    return self._hash
+
 
 class Address(Field):
   """

test/unit/client/link_protocol.py

@@ -30,7 +30,7 @@ class TestLinkProtocol(unittest.TestCase):
     self.assertEqual(7, protocol + 2)
     self.assertEqual(3, protocol - 2)
     self.assertEqual(15, protocol * 3)
-    self.assertEqual(1, protocol / 3)
+    self.assertEqual(1, protocol // 3)
 
   def test_equality(self):
     # LinkProtocols should be comparable with both other LinkProtocols and