drbd: Reduce the verbosity of some state transitions

State transitions in the space of non-allowed states used
to be very noisy. Reduce that, since that has little value
for the majority of the user base.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>