babeld: address FreeBSD "struct route" issue

FreeBSD system headers have their own "struct route", which made it
impossible to compile babeld. Switching babeld to "struct babel_route".
diff --git a/babeld/message.c b/babeld/message.c
index bfb1762..57d875f 100644
--- a/babeld/message.c
+++ b/babeld/message.c
@@ -854,7 +854,7 @@
 {
     babel_interface_nfo *babel_ifp = NULL;
     struct xroute *xroute;
-    struct route *route;
+    struct babel_route *route;
     const unsigned char *last_prefix = NULL;
     unsigned char last_plen = 0xFF;
     int i;
@@ -1004,7 +1004,7 @@
     if(ifp == NULL) {
       struct interface *ifp_aux;
       struct listnode *linklist_node = NULL;
-        struct route *route;
+        struct babel_route *route;
         FOR_ALL_INTERFACES(ifp_aux, linklist_node)
             send_update(ifp_aux, urgent, prefix, plen);
         if(prefix) {
@@ -1392,7 +1392,7 @@
                unsigned short seqno, const unsigned char *id)
 {
     struct xroute *xroute;
-    struct route *route;
+    struct babel_route *route;
     struct neighbour *successor = NULL;
 
     xroute = find_xroute(prefix, plen);
@@ -1438,7 +1438,7 @@
     if(!successor || successor == neigh) {
         /* We were about to forward a request to its requestor.  Try to
            find a different neighbour to forward the request to. */
-        struct route *other_route;
+        struct babel_route *other_route;
 
         other_route = find_best_route(prefix, plen, 0, neigh);
         if(other_route && route_metric(other_route) < INFINITY)