SilcSFTP silc_sftp_server_start(SilcSFTPSendPacketCallback send_packet,
                                    void *send_context,
                                    SilcSFTPFilesystem fs);

    Starts SFTP server and returns a context to it.  This function returns
    the allocated SFTP server context or NULL on error. The `send_packet'
    is called by the library when it needs to send a packet. The `fs' is the
    filesystem context allocated by the application.  Each socket connection
    should start its own server by calling this function.