Application callback to evaluate the cost of a newly discovered source. Set via the context attributes
setSourceCostCallback function.


- cbArg (Object)
- Callback object token
- topic (String)
- Topic for which the new source was discovered
- transport (LBMTransportSourceInfo)
- LBMTransportSourceInfo object describing the transport session
- hop_count (UInt32)
- Current hop count for the transport session
- cost (UInt32)
- Current cumulative cost for the transport session

Application-determined cost for this source as an unsigned 32-bit number.
To permanently reject this source, return LBM.LBM_SRC_COST_FUNCTION_REJECT