EXCHANGE_FLAG_NAT_T_KEEPALIVE
exchange->flags |= EXCHANGE_FLAG_NAT_T_KEEPALIVE;
if (exchange->flags & EXCHANGE_FLAG_NAT_T_KEEPALIVE)
exchange->flags |= EXCHANGE_FLAG_NAT_T_KEEPALIVE;
msg->exchange->flags |= EXCHANGE_FLAG_NAT_T_KEEPALIVE;