By Jack McEachen Ronnie O’Sullivan has threatened to walk away from snooker a few times down the years, but snooker legend Tony Knowles insists the opportunities afforded to the Rocket are why he remains at the table. O’Sullivan, now 48, remains at the top of his game and is eyeing a remarkable eighth World Championship at the Crucible this year. His quest comes after again threatening to quit last year, claiming he would depart the scene if he couldn’t play in China as much as he wanted, while also stating he might even switch to eight-ball. Knowles, who used to be world No. 2, had similar th…