Seattle Seahawks fullback Mack Strong has a spinal cord condition that is ending his career immediately — but not affecting his quality of life. And for that, the 36-year-old Pro Bowler, husband and father of two is grateful. “I’ve played a long time, 15 years. I felt like I was pretty lucky, pretty blessed,” a teary-eyed Strong said Monday after learning that a herniated disk in his neck is…