"realtek_destroy_ring() currently does nothing if
the card is operating
in legacy (pre-RTL8139C+) mode. In particular,
the producer and
consumer counters are incorrectly left holding their current
values.
Virtual hardware (e.g. the emulated RTL8139 in qemu and similar
VMs)
is tolerant of this behaviour, but real hardware will fail to
transmit
if the descriptors are not used in the correct order.
Fix by resetting the producer and consumer counters
in
realtek_destroy_ring() even if the card is operating in legacy
mode.