[connman] ofono: Don't cancel SetProperty("Active") calls

Next SetProperty("Active") won't succeed until the previous one completes.
Therefore it doesn't make sense to cancel these calls. Instead, connman
should wait for the completion of the pending SetProperty("Active") call
and then submit the next one if necessary.
Merge pull request #164 from monich/queue_active

ofono: Don't cancel SetProperty("Active") calls