Make deny & src-prefix actions work in install filter

src-prefix is about the 'from' option in ip-route. When the action value
matches exactly the source prefix of the route to install, the latter
is cleared at install. Otherwise, the route is not installed at all.

The purpose is mainly to provide a fallback for routers without support
of source-specific routes: only one route is kept, to a router that will
be able to route correctly.

TODO: man page

configuration.c

@@ -1511,12 +1511,8 @@ install_filter(const unsigned char *prefix, unsigned short plen,
                unsigned int ifindex,
                struct filter_result *result)
 {
-    int res;
-    res = do_filter(install_filters, NULL, prefix, plen,
+    return do_filter(install_filters, NULL, prefix, plen,
                      src_prefix, src_plen, NULL, ifindex, 0, result);
-    if(res < 0)
-        res = INFINITY;
-    return res;
 }
 
 int

disambiguation.c

@@ -215,7 +215,7 @@ is_installed(struct zone *zone)
 }
 
 static int
-change_route(int operation, const struct zone *zone,
+change_route(int operation, struct zone *zone,
              const struct babel_route *route, int metric,
              const unsigned char *new_next_hop,
              int new_ifindex, int new_metric)
@@ -227,8 +227,19 @@ change_route(int operation, const struct zone *zone,
     int m = install_filter(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen,
                            ifindex, &filter_result);
-    if (m < INFINITY)
+    if(m >= 0) {
+        if(m == INFINITY)
+            return 0;
+        if(filter_result.src_prefix) {
+            if(prefix_cmp(zone->src_prefix, zone->src_plen,
+                          filter_result.src_prefix, filter_result.src_plen)
+                    != PST_EQUALS)
+                return 0;
+            zone->src_plen = zone->src_plen >= 96 && v4mapped(zone->src_prefix)
+                ? 96 : 0;
+        }
         pref_src = filter_result.pref_src;
+    }
 
     int table = filter_result.table ? filter_result.table :
         find_table(zone->dst_prefix, zone->dst_plen,
@@ -242,21 +253,21 @@ change_route(int operation, const struct zone *zone,
 }
 
 static int
-add_route(const struct zone *zone, const struct babel_route *route)
+add_route(struct zone *zone, const struct babel_route *route)
 {
     return change_route(ROUTE_ADD, zone, route,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0);
 }
 
 static int
-del_route(const struct zone *zone, const struct babel_route *route)
+del_route(struct zone *zone, const struct babel_route *route)
 {
     return change_route(ROUTE_FLUSH, zone, route,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0);
 }
 
 static int
-chg_route(const struct zone *zone, const struct babel_route *old,
+chg_route(struct zone *zone, const struct babel_route *old,
           const struct babel_route *new)
 {
     return change_route(ROUTE_MODIFY, zone, old,
@@ -266,7 +277,7 @@ chg_route(const struct zone *zone, const struct babel_route *old,
 }
 
 static int
-chg_route_metric(const struct zone *zone, const struct babel_route *route,
+chg_route_metric(struct zone *zone, const struct babel_route *route,
                  int old_metric, int new_metric)
 {
     return change_route(ROUTE_MODIFY, zone, route,