cxgb4 : dcb open-lldp interop fixes

* In LLD_MANAGED mode, traffic classes were being returned in reverse order to
  lldp agent.
* Priotype of strict is no longer the default returned.
* Change behaviour of getdcbx() based on discussions on lldp-devel

These were missed as there was no working fetch interface for open-lldp when
running in LLD_MANAGED mode till now.

Fixes: 76bcb31e ("cxgb4 : Add DCBx support codebase and dcbnl_ops")

Signed-off-by: Anish Bhatt <anish@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>