tests: Make grpform_no_wsc_done more robust

It was possible for this test case to start a new group formation on
dev[1] while the first round was still going through the process of
processing group termination indication. That could result in the second
round failing unexpectedly.

Signed-off-by: Jouni Malinen <j@w1.fi>

tests/hwsim/test_p2p_grpform.py

@@ -856,6 +856,7 @@ def test_grpform_no_wsc_done(dev):
         if ev is None:
             raise Exception("Group formation timed out on P2P Client")
         dev[0].remove_group()
+        dev[1].wait_go_ending_session()
 
         if mode != "P2P GO - group formation":
             raise Exception("Unexpected mode on GO during group formation: " + mode)