[routing-manager] add feature to skip NS probe with router on same device (#8563)

This commit adds a new behavior in `RoutingManager` to skip performing
NS probe with a router with an address belonging to device infra
interface itself. This addresses the situation where platform may not
be be able to receive and pass the NA message responses from device
itself.

src/core/border_router/routing_manager.cpp

@@ -1752,6 +1752,18 @@ void RoutingManager::DiscoveredPrefixTable::HandleRouterTimer(void)
             continue;
         }
 
+        // If the `router` emitting RA has an address belonging to
+        // infra interface, it indicates that the RAs are from
+        // same device. In this case we skip performing NS probes.
+        // This addresses situation where platform may not be
+        // be able to receive and pass the NA message response
+        // from device itself.
+
+        if (Get<RoutingManager>().mInfraIf.HasAddress(router.mAddress))
+        {
+            continue;
+        }
+
         if (router.mTimeout <= now)
         {
             router.mNsProbeCount++;