fix some bugs in the example kernel and the Makefile entries.

netboot/etherboot.h

@@ -461,7 +461,6 @@ External prototypes
 /* main.c */
 #ifdef GRUB
 extern void print_network_configuration P((void));
-extern int arp_server_override P((const char *buf));
 extern int ifconfig P((char *ip, char *sm, char *gw, char *svr));
 #endif /* GRUB */