FDL master must check if token was received

[Rahix]

After the token was forwarded to the next active station, the FDL master must check whether this station has actually received the token and started making use of it.

[Rahix]

Initial check was added in commit bd48eaf ("fdl: master: Check if token was received after forwarding it") but behavior when the token was not received is not yet correct.

[Rahix]

And a testcase for this in commit aed674e ("fdl: tests: Add (disabled) testcase for token resend").