Via Velocity minimum MTU size

I'm trying to set the MTU size on my Via Velocity 6122 Gbit adapter from the default of 1500 down to 1492, but I keep getting this error:

[root@osprey ~]# ifconfig eth0 mtu 1492 SIOCSIFMTU: Invalid argument

Turns out that via-velocity.h defines the minimum MTU at 1500 bytes.

#define VELOCITY_MIN_MTU (1514-14) #define VELOCITY_MAX_MTU (9000)

And via-velocity.c enforces the limit.

if ((new_mtu < VELOCITY_MIN_MTU) || new_mtu > (VELOCITY_MAX_MTU)) { VELOCITY_PRT(MSG_LEVEL_ERR, KERN_NOTICE "%s: Invalid MTU.\n", vptr->dev->name); return -EINVAL; }

This is an Abit AV8 motherboard with an Athlon64 3000+ cpu running 2.6.16-1.2111_FC5 x86_64.

Can someone explain why the driver might constrain the NIC to a minimum MTU size of 1500?

Thanks, Jay