kernel-netlink: Don't fallback to peer address as gateway

This doesn't really seem useful (perhaps it was before we started to
configure the outbound interface on our routes). And it can actually
cause the route installation to fail e.g. for routes over point-to-point
interfaces where we'd get "Error: Nexthop has invalid gateway" errors.

Closes strongswan/strongswan#2548

src/libcharon/plugins/kernel_netlink/kernel_netlink_net.c

@@ -2075,10 +2075,6 @@ static host_t *get_route(private_kernel_netlink_net_t *this, host_t *dest,
 				*iface = get_interface_name_by_index(this, best->oif);
 			}
 		}
-		if (!addr && !match_net)
-		{	/* fallback to destination address */
-			addr = dest->clone(dest);
-		}
 	}
 	else
 	{