skypiax: when trying to specify the use of an already busy interface for originating an outbound call, return SWITCH_CAUSE_NORMAL_CIRCUIT_CONGESTION instead of DESTINATION_OUT_OF_ORDER. Like in openzap. Would be better to return SWITCH_CAUSE_REQUESTED_CHAN_UNAVAIL ???

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@16893 d0543943-73ff-0310-b7d9-9358b9ac24b2