Fixes typos in tempest/api

Just some typos

Change-Id: I062b60e6b20bb116547f613556cf976d58f81d40
diff --git a/tempest/api/network/test_routers.py b/tempest/api/network/test_routers.py
index 9f8c742..8b939fe 100644
--- a/tempest/api/network/test_routers.py
+++ b/tempest/api/network/test_routers.py
@@ -97,7 +97,7 @@
         name = rand_name('router-')
         resp, create_body = self.client.create_router(name)
         self.addCleanup(self.client.delete_router, create_body['router']['id'])
-        # Add router interafce with subnet id
+        # Add router interface with subnet id
         resp, interface = self.client.add_router_interface_with_subnet_id(
             create_body['router']['id'], subnet['id'])
         self.assertEqual('200', resp['status'])