Make src-prefix action work in install filter

The purpose is to override *locally* RTA_SRC ('from' option in ip-route).

babeld.man

@@ -578,7 +578,7 @@ For a redistribute filter, redistribute this route with metric
 .IR value .
 .TP
 .BI src-prefix " prefix"
-For a redistribute filter, set the source prefix of this route to
+For a redistribute or install filter, set the source prefix of this route to
 .IR prefix .
 .TP
 .BI table " table"

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)
@@ -223,16 +223,24 @@ change_route(int operation, const struct zone *zone,
     struct filter_result filter_result;
     unsigned char *pref_src = NULL;
     unsigned int ifindex = route->neigh->ifp->ifindex;
+    int table;
 
     int m = install_filter(zone->dst_prefix, zone->dst_plen,
                            zone->src_prefix, zone->src_plen,
                            ifindex, &filter_result);
-    if (m < INFINITY)
+    if (m < INFINITY) {
         pref_src = filter_result.pref_src;
-
-    int table = filter_result.table ? filter_result.table :
-        find_table(zone->dst_prefix, zone->dst_plen,
-                   zone->src_prefix, zone->src_plen);
+        if(filter_result.src_prefix) {
+            zone->src_prefix = filter_result.src_prefix;
+            zone->src_plen = filter_result.src_plen;
+        }
+        table = filter_result.table;
+    } else {
+        table = 0;
+    }
+    if (!table)
+        table = find_table(zone->dst_prefix, zone->dst_plen,
+                           zone->src_prefix, zone->src_plen);
 
     return kernel_route(operation, table, zone->dst_prefix, zone->dst_plen,
                         zone->src_prefix, zone->src_plen, pref_src,
@@ -242,21 +250,21 @@ 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 +274,7 @@ 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,