Added support for static ARP table entries (added option ETHARP_SUPPORT_STATIC_ENTRIES) (+ added test); refactored the etharp code a bit

test/unit/lwip_unittests.c

@@ -4,6 +4,7 @@
 #include "tcp/test_tcp.h"
 #include "tcp/test_tcp_oos.h"
 #include "core/test_mem.h"
+#include "etharp/test_etharp.h"
 
 #include "lwip/init.h"
 
@@ -18,6 +19,7 @@ int main()
     tcp_suite,
     tcp_oos_suite,
     mem_suite,
+    etharp_suite,
   };
   size_t num = sizeof(suites)/sizeof(void*);
   LWIP_ASSERT("No suites defined", num > 0);