periodically clean up timed-out sessions and old signatures, instead of trying to do it when creating new sessions or adding new signatures

src/yggdrasil/router.go

@@ -101,6 +101,8 @@ func (r *router) mainLoop() {
 				// Any periodic maintenance stuff goes here
 				r.core.switchTable.doMaintenance()
 				r.core.dht.doMaintenance()
+				r.core.sessions.cleanup()
+				r.core.sigs.cleanup()
 				util_getBytes() // To slowly drain things
 			}
 		case f := <-r.admin: