section 8 merge requirement 2 and 3

[Xavier Vilajosana]

10. I think the information in section 8 would be more generally useful if not stated in terms of a queue-based implementation:

A node must not transmit frames containing higher-layer packets until the node has successfully joined a network.

Frames generated by the IEEE 802.15.4 layer are transmitted before frames containing higher-layer packets.

Frame types BEACON and COMMAND are transmitted before frame types DATA and ACK.

A node has to be prepared to send a BEACON or COMMAND frame at any time.

I've tried to infer the desired behavior from the description of queue usage. If I understand the original text correctly, there is no difference between the second and third requirements.

TW> Editorial. TW> @Editor, please merge requirements 2 and 3.