Python3 tests: Fix asserts.

Use assert(Not)Equal()
Use assert{Greater,Less}[Equal]

Change-Id: I7c14570b8dce463ee13a67e9c1f10beb1a0308a8
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>

test/test_ip6.py

@@ -1920,8 +1920,8 @@ class TestIP6Punt(VppTestCase):
         # but not equal to the number sent, since some were policed
         #
         rx = self.pg1._get_capture(1)
-        self.assertTrue(len(rx) > 0)
-        self.assertTrue(len(rx) < len(pkts))
+        self.assertGreater(len(rx), 0)
+        self.assertLess(len(rx), len(pkts))
 
         #
         # remove the poilcer. back to full rx