cxgb4: Initialize data structures before using.

We should not assume reserve fields to be don't cares as fields may change.
Clearing data structures before using.

Signed-off-by: Jay Hernandez <jay@chelsio.com>
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>