This ensures struct netif doesn't contain 'rs_count' if LWIP_IPV6 is disabled but LWIP_IPV6_SEND_ROUTER_SOLICIT is at its default. See bug #56509
This ensures struct netif doesn't contain 'rs_count' if LWIP_IPV6 is disabled but LWIP_IPV6_SEND_ROUTER_SOLICIT is at its default. See bug #56509