It seems that your SFP has incorrect data burned in it’s EEPROM memory and Linux cannot recognize what mode should it put the network interface into. This is rather common for SFP modules, unfortunately.
Could you send the contenst of your SFP’s EEPROM? This can be done via the command
ethtool -m sfp raw on | hexdump -C
It is possible that you will have to install the ethtool utility
opkg update
opkg install ethtool