cxgbe: fix minimum descriptors requirement

cxgbe: fix minimum descriptors requirement

Most dpdk examples and apps seem to initialize with a minimum of 128 rx
descriptors and 512 tx descriptors for queue setup.  However, CXGBE PMD
enforces a minimum of 1024 descriptors.  This causes the dpdk stack
to return -EINVAL because the apps do not request the minimum required.

The fix is to relax this enforcing in CXGBE PMD. A minimum of 128
descriptors seems to be a good number with the least impact on the
performance.

Fixes: 946c9ed95616 ("cxgbe: get descriptor limits")

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>