By Chris Rosvoglou Once free agency officially opened, Jalen Brunson signed a four-year contract with the Knicks. Of course, this was a tough pill to swallow for the Mavericks. It was reported that Dallas was “frustrated” that reports of Brunson leaving for New York came out prior to its scheduled conversations with the Villanova product. “From what I’ve gathered, the Mavericks are quite frustrated with the Knicks — and not just because reports of a finished deal came out before New York was even allowed to speak with Brunson (though I am not sure how tampering rules account for father-son rel…