vport_profile_conf: Resolve memory leak found by Valgrind

The 'virtPortInterfaceID' was not VIR_FREE()'d

src/conf/netdev_vport_profile_conf.c

@@ -198,6 +198,7 @@ cleanup:
     VIR_FREE(virtPortInstanceID);
     VIR_FREE(virtPortProfileID);
     VIR_FREE(virtPortType);
+    VIR_FREE(virtPortInterfaceID);
 
     return virtPort;