Replace tap interface using general interface

Change-Id: Icd73f00162fb6aabe296c8bb6f2174ad4f6a17b7
Signed-off-by: Hongjun Ni <hongjun.ni@intel.com>
diff --git a/test/test_pppoe.py b/test/test_pppoe.py
index 1d0aeff..13499a3 100644
--- a/test/test_pppoe.py
+++ b/test/test_pppoe.py
@@ -343,7 +343,7 @@
         # and we should still be able to use the original
         #
         try:
-            gre_if.add_vpp_config()
+            pppoe_if.add_vpp_config()
         except Exception:
             pass
         else:
@@ -400,7 +400,7 @@
         # and we should still be able to use the original
         #
         try:
-            gre_if.remove_vpp_config()
+            pppoe_if.remove_vpp_config()
         except Exception:
             pass
         else: