The lobby was packed with high school students — freshmen, sophomores, juniors and seniors from Greenport, Southold and Mattituck. Clustered in groups of four and five, they laughed and chatted like teenagers do.But this wasn’t the lobby of a movie theater or some ice skating rink, and you couldn’t tell the difference between a kid from Mattituck and a kid from Southold. These young adults, almost 200 of them, were getting ready for their annual Naval Junior Reserve Officers Training Corps inspection at Southold High School. Less