Suing a patent troll for GPL violations is impossible by definition. A patent troll is a non-practicing entity, so they don't produce anything (but lawsuits) and thus they don't distribute software and conversely can't be sued for GPL violations.
If whatever company that is suing on patent grounds is also producing software (like this current case), then they are not a patent troll by the most common definition of the term but just plain aholes.
Nah, a patent troll is anyone who trolls with patents. That doesn't need to be the only thing they do. The classic example, SCO, had actual products which weren't related in any way to their patent suits.
No, a patent troll is a non-practicing entity (NPE). The specific reason they're dangerous is because they aren't subject to counter claims. You can't come along and redefine a word simply because you don't understand it.
The term is fairly new and as such the common definition is still changing, but Wikipedia agrees with regularfry
Patent troll is a pejorative term used for a person or company who enforces patents against one or more alleged infringers in a manner considered aggressive or opportunistic with no intention to manufacture or market the patented invention.*
If whatever company that is suing on patent grounds is also producing software (like this current case), then they are not a patent troll by the most common definition of the term but just plain aholes.