Include BigSwitch plugin options in ML2 page

Adds a link to the Big Switch plugin config
options on the ML2 page since it can be loaded
as an ML2 driver as well.

Change-Id: I6af4a2dfbae16c626e20c89e9edbd6d019ef8027
Implements: blueprint bigswitch-ml2-plugin
Merge "Include BigSwitch plugin options in ML2 page"