GattClient: Add test for requestMtu

Some test are ignored and associated bug has been opened

Bug: 303249734
Bug: 308031848
Bug: 308014302
Bug: 307981748
Test: atest BumbleBluetoothTests:android.bluetooth.GattClientTest
Change-Id: Id4a06157d388aca0cb67dfff8d61f1c3ed4524d7