Fix Quantenna interface suffix.

Change-Id: Ie4cc500521353189e09f2bdd83ed182dda9f6392
diff --git a/wifi/quantenna.py b/wifi/quantenna.py
index 1408574..f1d5da5 100755
--- a/wifi/quantenna.py
+++ b/wifi/quantenna.py
@@ -40,7 +40,6 @@
   # IDs start at 2). The client interface must map to wifi0, so it must have
   # VLAN ID 2.
   prefix = 'wlan' if mode == 'ap' else 'wcli'
-  suffix = '_' + suffix if suffix else ''
   for hif in _get_quantenna_interfaces():
     if re.match(prefix + r'\d*' + suffix, hif):
       vlan = _get_vlan(hif)
diff --git a/wifi/quantenna_test.py b/wifi/quantenna_test.py
index 177f557..b0fb485 100755
--- a/wifi/quantenna_test.py
+++ b/wifi/quantenna_test.py
@@ -35,7 +35,7 @@
   quantenna._get_vlan = lambda _: 3
   wvtest.WVPASSEQ(quantenna._get_interface('ap', ''),
                   ('wlan0', 'wifi1', '00:00:00:00:00:00', 3))
-  wvtest.WVPASSEQ(quantenna._get_interface('ap', 'portal'),
+  wvtest.WVPASSEQ(quantenna._get_interface('ap', '_portal'),
                   ('wlan0_portal', 'wifi1', '00:00:00:00:00:00', 3))
   wvtest.WVPASSEQ(quantenna._get_interface('sta', ''),
                   (None, None, None, None))