fix aggressive expiration detection (#11446)

for some flaky networks this may be too fast of a value
choose a defensive value, and let this be addressed
properly in a new refactor of dsync with renewal logic.

Also enable faster fallback delay to cater for misconfigured
IPv6 servers

refer
 - https://golang.org/pkg/net/#Dialer
 - https://tools.ietf.org/html/rfc6555

cmd/lock-rest-server.go

@@ -302,7 +302,7 @@ func lockMaintenance(ctx context.Context, interval time.Duration) error {
 		for _, c := range lockers {
 			go func(lrip lockRequesterInfo, c dsync.NetLocker) {
 				defer wg.Done()
-				ctx, cancel := context.WithTimeout(GlobalContext, 3*time.Second)
+				ctx, cancel := context.WithTimeout(GlobalContext, 5*time.Second)
 
 				// Call back to all participating servers, verify
 				// if each of those servers think lock is still