This also avoids a potential buffer overflow in case the very first
receive descriptor fails to allocate, as an index of -1 would be used
afterwards. Kudos to Roel Kluin for pointing this out and providing an
initial patch.
Signed-off-by: NPhil Sutter <n0-1@freewrt.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>