ehea: Reduce memory usage in buffer pools

Now that we enable multiqueue by default the ehea driver is using
quite a lot of memory for its buffer pools. With 4 queues we
consume 64MB in the jumbo packet ring, 16MB in the medium packet
ring and 16MB in the tiny packet ring.

We should only fill the jumbo ring once the MTU is increased but
for now halve it's size so it consumes 32MB. Also reduce the tiny
packet ring, with 4 queues we had 16k entries which is overkill.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>