opt.h, tcpip.c: New configuration option LWIP_ARP allow to disable ARP init at build time if you only use PPP or SLIP. The default is enable. Note we don't have to call etharp_init in your port's initilization sequence if you use tcpip.c, because this call is done in tcpip_init function.

src/include/lwip/opt.h

@@ -165,6 +165,10 @@ a lot of data that needs to be copied, this should be set high. */
 #endif
 
 /* ---------- ARP options ---------- */
+#ifndef LWIP_ARP
+#define LWIP_ARP                        1
+#endif
+
 /** Number of active hardware address, IP address pairs cached */
 #ifndef ARP_TABLE_SIZE
 #define ARP_TABLE_SIZE                  10