cxgbi: use per-connection link-speed dependent send/recv windows

For adapters supporting both 10G and 40G use per-connection send/recv window
and calculate the size based on the link speed.

Signed-off-by: Karen Xie <kxie@chelsio.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Odin.com>