[PATCH] skge: don't allow transmit ring to be too small

The driver will get stuck (permanent transmit timeout), if the transmit
ring size is set too small.  It needs to have enough ring elements to
hold one maximum size transmit.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>