Hello,
I have project where I am using jumbo frames for communication with GigE Digital Cameras.
For this reason I installed patch-632-CE-CN-Milestone-Fn under QNX 632. Using this patch I am modifying the MTU by 
command:"ifconfig wm0 mtu 9000".
In QNX 632 this works fine,
Recently I installed QNX 641 on the same hardware, but the command above fails with message: "ifconfig: SIOCSIFMTU: 
Invalid argument", although it is supposed to work.
The chipset used is Intel 82573L, and I am starting io-pkt with:

io-pkt-v4 -di82544 -pqnet tx_retries=1 periodic_ticks=10
waitfor /dev/socket
ifconfig wm0 ip4csum tcp4csum udp4csum
ifconfig wm0 mtu 9000
ifconfig wm0 10.0.0.1

Driver used is: devnp-i82544.so

Why in QNX6.4.1 MTU modification does not work?