feat: don't gc client rpc connection if ExpireTime is 0 (#1296)

In case we don't want to GC client connections in some special
circumstances.

Signed-off-by: Eryu Guan <eguan@linux.alibaba.com>

pkg/rpc/client_util.go

@@ -65,7 +65,7 @@ func (conn *Connection) startGC() {
 				serverNode := node.(string)
 				totalNodeSize++
 				atime := accessTime.(time.Time)
-				if time.Since(atime) < conn.connExpireTime {
+				if conn.connExpireTime == 0 || time.Since(atime) < conn.connExpireTime {
 					return true
 				}
 				conn.gcConn(serverNode)