I have a R610 AP connected to an ICX-7150-C12P switch using unleashed. The AP set up as a member AP and is connected via Cat6 to the switch. The AP connects at 100 Mbps whereas the Master AP is connecting at 1 Gbps. I tried to configure the port using "speed-duplex 1000-full" via telnet but that caused the port completely lose the connection (so I set the port back to auto). Not sure what else to try since the AP and switch should support full 1 Gbps.
It is also good to try with different port on the switch, just to ensure.
Below command can help you from the AP side: "get eth" will tell you the supported speed of the AP ethernet. "set ethspeed eth0 auto" will ensure to connect the AP eth0 to negotiate to the max supported.