qlge: Allow RX buf rings to be > than 4096 bytes.

RX buffer rings can be comprised of non-contiguous fixed
size chunks of memory. The ring is given to the hardware
as a pointer to a location that stores the location of
the queue.  If the queue is greater than 4096 bytes then
the hardware gets a list of said pointers.
This patch addes the necessary logic to generate the list if
the queue size exceeds 4096.

Signed-off-by: Ron Mercer <ron.mercer@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>