Enable Maple OLT adapter to receive inband packet-in messages via frameio.

Change-Id: Ic989fa34459dbc3295b4c46282d35047a839862e
diff --git a/voltha/adapters/maple_olt/maple_olt.py b/voltha/adapters/maple_olt/maple_olt.py
index 2ffa795..a50a732 100644
--- a/voltha/adapters/maple_olt/maple_olt.py
+++ b/voltha/adapters/maple_olt/maple_olt.py
@@ -405,9 +405,9 @@
             )
 
         # finally, open the frameio port to receive in-band packet_in messages
-        self.log.info('registering-frameoi')
-        # self.io_port = registry('frameio').add_interface(
-        #    self.interface, self.rcv_io, is_inband_frame)
+        self.log.info('registering-frameio')
+        self.io_port = registry('frameio').add_interface(
+            self.interface, self.rcv_io, is_inband_frame)
 
     def rcv_io(self, port, frame):
         self.log.info('reveived', iface_name=port.iface_name,