BOSTON — The killing of a Massachusetts police officer has some Republicans calling for the reinstatement of the death penalty for the murder of law enforcement officers.Recent attempts to restore capital punishment in the state have faltered, most recently after the killing of another police officer two years ago and in 2013, after the Boston Marathon bombing.The death of Sean Gannon, a Yarmouth K-9 officer who was fatally shot in the head while serving an arrest warrant last Thursday, has again raised the issue.