VPP-1508 python3 tests: .encode('hex')

Change to binascii.hexlify() for consistent bahavior.

Change-Id: Ie430cdd1ffeb6510db4aa037546e42d85992093b
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/test_classifier_ip6.py b/test/test_classifier_ip6.py
index 9f4c20a..cbcf5c4 100644
--- a/test/test_classifier_ip6.py
+++ b/test/test_classifier_ip6.py
@@ -184,9 +184,11 @@
         :param int dst_port: destination port number "x"
         """
         if src_ip:
-            src_ip = socket.inet_pton(socket.AF_INET6, src_ip).encode('hex')
+            src_ip = binascii.hexlify(socket.inet_pton(
+                socket.AF_INET6, src_ip))
         if dst_ip:
-            dst_ip = socket.inet_pton(socket.AF_INET6, dst_ip).encode('hex')
+            dst_ip = binascii.hexlify(socket.inet_pton(
+                socket.AF_INET6, dst_ip))
 
         return ('{:0>14}{:0>34}{:0>32}{:0>4}{:0>4}'.format(
             hex(nh)[2:], src_ip, dst_ip, hex(src_port)[2:],