By Tzvi Machlin The Pittsburgh Steelers had their lowest-ranked defense in over 30 years this past season. So they’re bringing in a veteran linebacker who they hope can turn things around. On Friday, the Steelers announced that linebacker Robert Spillane has signed a one-year restricted free agent tender. Spillane returns to the Steelers for a fourth straight season, where he plays on both defense and special teams. Last year saw Spillane get the most playing time of his young career. The former Western Michigan linebacker had 56 tackles in 14 games and had four starts which mostly came toward…