cxgb3: sge setup fixes

Enable timestamps, update delayed ack threshold for iSCSI/iWARP traffic
Remove the len flag in Tx requests. It might corrupt offload trace packets.
Update SGE context setup to avoid potential H/W misprogrammation.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>