pgbench: Avoid unnecessary measurement of connection delays.

Commit 547f04e7 changed pgbench so that it used the measurement result
of connection delays in its benchmark report only when -C/--connect option
is specified. But previously those delays were unnecessarily measured
even when that option is not specified. Which was a waste of cycles.
This commit improves pgbench so that it avoids such unnecessary measurement.

Back-patch to v14 where commit 547f04e7 first appeared.

Author: Yugo Nagata
Reviewed-by: Fabien COELHO, Asif Rehman, Fujii Masao
Discussion: https://postgr.es/m/20210614151155.a393bc7d8fed183e38c9f52a@sraoss.co.jp

src/bin/pgbench/pgbench.c

@@ -6622,6 +6622,7 @@ threadRun(void *arg)
 
 	thread_start = pg_time_now();
 	thread->started_time = thread_start;
+	thread->conn_duration = 0;
 	last_report = thread_start;
 	next_report = last_report + (int64) 1000000 * progress;
 
@@ -6645,14 +6646,6 @@ threadRun(void *arg)
 				goto done;
 			}
 		}
-
-		/* compute connection delay */
-		thread->conn_duration = pg_time_now() - thread->started_time;
-	}
-	else
-	{
-		/* no connection delay to record */
-		thread->conn_duration = 0;
 	}
 
 	/* GO */