Fabric: Fix get_link_stats to match Node.get_fabric_link_stats()
Fabric: Fix get_link_stats to match Node.get_fabric_link_stats()

For commands that run across all nodes, we want the interface of
Fabric and Node to be very similar.

This means Fabric.get_link_stats now takes a "link" parameter as
well, instead of returning results for all links.

Cynerva/cxmanage,SilverLiningSystems/cxmanage-test,SLS-Dev/cxmanage,SilverLiningSystems/cxmanage-test,SilverLiningSystems/cxmanage-test2,SLS-Dev/cxmanage,SilverLiningSystems/cxmanage-test2,Cynerva/cxmanage