wrap scapy with explicit imports

pylint can't handle scapy's magical imports.
diff --git a/tests-1.3/match.py b/tests-1.3/match.py
index c807ee8..c45858f 100644
--- a/tests-1.3/match.py
+++ b/tests-1.3/match.py
@@ -13,7 +13,7 @@
 from oftest import config
 import oftest.base_tests as base_tests
 import ofp
-import scapy.all as scapy
+import oftest.packet as scapy
 
 from oftest.testutils import *
 from oftest.parse import parse_ipv6