NEW YORK — Speaking to reporters on Friday for the first time since the nerve impingement in his lower back was diagnosed, Ben Simmons said the last few weeks have been among the most frustrating of his career. He wants to compete. He wishes he was available to help pull the Nets out of their recent slump. Simmons, who has not appeared in a game for Brooklyn since Nov. 6, is managing the best he can. The 6-foot-10 guard cannot control what happens to his body in the heat of competition. No one can. But he can control his mindset and the effort he puts forth each day in rehab. Friday marked the…