Branch b1_6

b=15069
i=rread
i=wangdi

remove LASSERT in ptlrpc_invalidate_import() since ping req can be queued even
imp_invalid is set. See also bug 15716.

lustre/ptlrpc/import.c

@@ -234,7 +234,6 @@ void ptlrpc_invalidate_import(struct obd_import *imp)
                         DEBUG_REQ(D_ERROR, req, "still on delayed list");
                 }
                 spin_unlock(&imp->imp_lock);
-                LASSERT(atomic_read(&imp->imp_inflight) == 0);
         }
 
   out: