I installed SFOS 17 on a intel celeron system with 2 realteks nics and I noticed that webadmin does not support configuring the ethernet ports after the 2 ports are combined into a transparent bridge.
The port speed can only be changed by accessing the console via web admin and giving the following commands:
console> set network interface-speed Port1 speed 1000fd
console> set network interface-speed Port2 speed 1000fd
(Log in to the CLI using Telnet or SSH. You can also access the CLI from admin > Console in the upper right corner of the Admin Console screen. Choose option 4. Device Console.)