[En-Nut-Discussion] External interrupts on Ethernut 3

[Petri Hyötylä]

I forgot the CAN_SIGNAL definitions.

#ifdef ETHERNUT2
#define CAN_SIGNAL sig_INTERRUPT7 // CAN interrupt
#endif

#ifdef ETHERNUT3
#define CAN_SIGNAL sig_FIQ // CAN interrupt
#endif

#define CAN_SIGNAL_BIT 7