liquidio: fix inaccurate count of napi-processed rx packets reported to Octeon

lio_enable_irq (called by napi poll) is reporting to Octeon an inaccurate
count of processed rx packets causing Octeon to eventually stop forwarding
packets to the host.  Fix it by using this formula for an accurate count:

    processed rx packets = droq->pkt_count - droq->pkts_pending

Also increase SOFT_COMMAND_BUFFER_SIZE to match what the firmware expects.

Signed-off-by: Prasad Kanneganti <prasad.kanneganti@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>