Specify the QoS level to be used when publishing the Will Message.
If the Will Flag is set to 0, then the Will QoS MUST be set to 0 (0x00).
If the Will Flag is set to 1, the value of Will QoS can be 0 (0x00), 1 (0x01), or 2 (0x02).
It MUST NOT be 3 (0x03)
Specify the QoS level to be used when publishing the Will Message.
If the Will Flag is set to 0, then the Will QoS MUST be set to 0 (0x00). If the Will Flag is set to 1, the value of Will QoS can be 0 (0x00), 1 (0x01), or 2 (0x02). It MUST NOT be 3 (0x03)