Huge performance degradation for UDP between kernel 2.4.17 and 2.6.x

Hi

I'm having a big issue with UDP. Using a powerpc board (MPC860).

With our board running kernel 2.4.17, I'm able to send 160000 voice 
packets (UDP, 96 bytes per packet) in 11 seconds.
With the same board running either Kernel 2.6.35.14 or Kernel 3.4.7, I 
need 55 seconds to send the same amount of packets.


Is there anything to tune in order to get same output rate as with 
Kernel 2.4 ?

Regards
Christophe