> +/*
> + * This function is just taken and modified from bge(4) driver.
> + *
> + * Although re(4) chips support auto-padding small packets,
> + * but it seems to cause a bug on IPv4 hardware checksum offload.
> + * To avoid the bug, pad packets manually if ip4csum is enabled.
> + */

i'm not sure if it's a good idea to allocate a mbuf for this purpose.
an alternative would be to set up a dummy descriptor which
points (system-global?) zero'ed memory.

YAMAMOTO Takashi