Firmware release v.R1.49 for DAS-3248DC rev.B1

Release notes:

1. Add IGMP filter by default.
2. Default value of IGMP-snooping port status is enabled and IGMP-snooping status is disabled.
3. Add tab auto complete function in CLI.
4. Fix get atur physical layer information may cause system internal error.
5. Fix get line interface from telnet may cause crash from telnet.