Yes you were right. Just found the solution, just comment RemoteBindAddress in firebird.conf & restart firebird service and it works.
By the way, for a small database, firebird server performance on Raspberry Pi2 is not bad at all. With my microSD (read speed about 20MB/s), it took about 2 secs to retrieve data from store procedure while on my cpu(Phenom X6 3.0GHz) took 0.2 secs. It will use as a 24/7 server for data collection only, i think, performance is enough. Regards, Agus