this is not possible.
The function does not exist.
You could write scripts and suspend services receiving too much traffic, but this seems quite complex.
Also, I don't see why you would want to limit conn/sec.
Normally, you should translate the conn/sec rate into a maxconn.
For example, if it takes 10 sec to send the requested page in average and the box dies if the rate is 1000 conn/sec, then configure a maxconn of 1000 x 10 / 2 = 5000 should prevent the server to block.
Regards,
Gilles.