Randomize anti-fee sniping height

"When possible to use anti fee-sniping, you always set the current height. All implementations of anti fee-sniping i'm aware of randomize this by sometimes using a much lower height (typically 100 less) to avoid consistently giving up the height at which a transaction was crafted. I'm not sure how useful this randomization is, but you might want to consider it. Especially as you already have a RNG at hand in this function."