Ensure master entering the bus passes token correctly from the beginning

[Rahix]

Right now, when a master enters the bus, it does not know who is the next master to pass the token to. Thus, it will self-pass the token until its GAP update cycle leads to the next master being re-discovered.

This means that the new master entering the bus blocks all communication from other masters until its first GAP cycle has completed. A better mechanism is needed here to ensure other masters can continue operating properly.