The LWIP example (inetd) ship with only GigE 10/100/1000 interface supported.
To switch support to the (10/100) interface, the example needs to be rebuilt with the following change in lwip_sysboot_task.h.
#if 0 // ADSP-SC5xx family gemac 10/100/1000
#define EMAC_DRIVER_ENTRY (GEMAC0DriverEntry) /* EMAC0 Driver Entry point */
#else // ADSP-SC5xx family emac 10/100
#define EMAC_DRIVER_ENTRY (GEMAC1DriverEntry) /* EMAC1 Driver Entry point */
#endif