Added and updated debugging printouts and reformatted code to make it a little easier to read.

core/net/uip-debug.c

@@ -43,6 +43,10 @@
 void
 uip_debug_ipaddr_print(const uip_ipaddr_t *addr)
 {
+  if(addr == NULL || addr->u8 == NULL) {
+    printf("(NULL IP addr)");
+    return;
+  }
 #if UIP_CONF_IPV6
   uint16_t a;
   unsigned int i;