fix(mon-pages): underline a value only on hover

The cell's own rule underlines every anchor it holds, and being nested
it outranked the rule meant to take that off a highlighted value. So
the service counts read as links at rest, where the design underlines
them only under the pointer.

The exception now sits beside the rule it overrides, where it outranks
it, and the hover underline follows the value's own colour.

CMK-38149

Change-Id: I623e899fee225b45691de86d3e56125ce6743b31