Fix exporting of IPv4 default routes on recent kernels.

Recent kernels don't include RTA_DST in the default route.  This fixes
incorrect parsing of such entries.  Reported by Robert Lukan.

kernel_netlink.c

@@ -784,7 +784,12 @@ parse_kernel_route_rta(struct rtmsg *rtm, int len, struct kernel_route *route)
     memset(&route->prefix, 0, sizeof(struct in6_addr));
     memset(&route->gw, 0, sizeof(struct in6_addr));
     route->plen = rtm->rtm_dst_len;
-    if(rtm->rtm_family == AF_INET) route->plen += 96;
+    if(rtm->rtm_family == AF_INET) {
+        const char zeroes[4] = {0, 0, 0, 0};
+        v4tov6(route->prefix, zeroes);
+        route->plen += 96;
+    }
+
     route->metric = KERNEL_INFINITY;
     route->ifindex = 0;
     route->proto = rtm->rtm_protocol;

util.c

@@ -223,7 +223,7 @@ mask_prefix(unsigned char *ret,
     return (const unsigned char *)ret;
 }
 
-static unsigned char v4prefix[16] =
+static const unsigned char v4prefix[16] =
     {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xFF, 0xFF, 0, 0, 0, 0 };
 
 const char *