platform: don't check for route existence (fixup)

This was part of a patch that resulted in commit 5dd15bd but
unfortunately also part of a reverted patch 42b4323. We need
to add it back.

src/platform/nm-linux-platform.c

@@ -244,7 +244,7 @@ add_kernel_object (struct nl_sock *sock, struct nl_object *object)
 		return rtnl_addr_add (sock, (struct rtnl_addr *) object, NLM_F_CREATE | NLM_F_REPLACE);
 	case IP4_ROUTE:
 	case IP6_ROUTE:
-		return rtnl_route_add (sock, (struct rtnl_route *) object, NLM_F_CREATE);
+		return rtnl_route_add (sock, (struct rtnl_route *) object, NLM_F_CREATE | NLM_F_REPLACE);
 	default:
 		g_assert_not_reached ();
 	}