WASHINGTON — The F-15 fighter that was shot down over southwestern Iran last month and set off a dangerous rescue mission was probably struck by a Chinese-made shoulder-launched missile, three people with knowledge of the matter told NBC News. Subscribe to read this story ad-free Get unlimited access to ad-free articles and exclusive content.In the early days of the conflict, China also may have provided Iran with a long-range early-warning radar that spots stealth aircraft that are meant to evade detection, according to one of the people and a U.S. official with knowledge of the matter. U.S. officials are still…