fix(iot-dev): Fix AMQP layer not releasing a semaphore for method lin…

…ks after unsubscribing from methods (#1831)

This semaphore was just never released in this method

iothub/device/src/Transport/Amqp/AmqpUnit.cs

@@ -619,6 +619,7 @@ public async Task DisableMethodsAsync(TimeSpan timeout)
             finally
             {
                 Logging.Exit(this, timeout, nameof(DisableMethodsAsync));
+                _methodLinkSemaphore.Release();
             }
         }