[communication] Improves debug message sending.
* Renames cb_debugAddrSignal(sMsg *) in sb_debugUpdateAddr(sMsg *) and sb_debugSignalling(sb_Address) in sb_debugSendAddr(sb_Address).
* Adds a default debug address ADDR_DEBUG_DFLT  (has to be set in network_cfg.h).
* Corrects and improves the chained list for sb_attache() and sb_receive().