Use use_lchan/put_lchan for call handling to keep the channel up

Increase when the refcount of the lchan when we initiate a call,
get a SETUP message and put it when we want to release the call...

Once we have proper Q.931 support the use/put needs to be improved,
e.g. we currently do not allow to hangup from the network, and it
will ring until the end of time...