vxge: Fix starvation of receive ring controller when blasted by short packets.

- Fix starvation of receive ring controller when blasted by short packets. This was because the driver was posting 64 rxds initially while the ring controller
was expecting to read 256 replenished rxds. While the driver was coming up,
the internal rxd memory filled up the 64 buffers provided and the ring
controller was left waiting for the remaining 192 rxds to complete the write
back of completed rxds to the host and generation of an interrupt.

Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@neterion.com>
Signed-off-by: Ramkrishna Vepa <ram.vepa@neterion.com>
Signed-off-by: David S. Miller <davem@davemloft.net>