lock: improve locker initialization at init (#8776)

Use reference format to initialize lockers
during startup, also handle `nil` for NetLocker
in dsync and remove *errorLocker* implementation

Add further tuning parameters such as

 - DialTimeout is now 15 seconds from 30 seconds
 - KeepAliveTimeout is not 20 seconds, 5 seconds
   more than default 15 seconds
 - ResponseHeaderTimeout to 10 seconds
 - ExpectContinueTimeout is reduced to 3 seconds
 - DualStack is enabled by default remove setting
   it to `true`
 - Reduce IdleConnTimeout to 30 seconds from
   1 minute to avoid idleConn build up

Fixes #8773

cmd/local-locker.go

@@ -17,7 +17,6 @@
 package cmd
 
 import (
-	"errors"
 	"fmt"
 	"sync"
 	"time"
@@ -39,40 +38,6 @@ func isWriteLock(lri []lockRequesterInfo) bool {
 	return len(lri) == 1 && lri[0].Writer
 }
 
-type errorLocker struct{}
-
-func (d *errorLocker) String() string {
-	return ""
-}
-
-func (d *errorLocker) Lock(args dsync.LockArgs) (reply bool, err error) {
-	return false, errors.New("unable to lock")
-}
-
-func (d *errorLocker) Unlock(args dsync.LockArgs) (reply bool, err error) {
-	return false, errors.New("unable to unlock")
-}
-
-func (d *errorLocker) RLock(args dsync.LockArgs) (reply bool, err error) {
-	return false, errors.New("unable to rlock")
-}
-
-func (d *errorLocker) RUnlock(args dsync.LockArgs) (reply bool, err error) {
-	return false, errors.New("unable to runlock")
-}
-
-func (d *errorLocker) Close() error {
-	return nil
-}
-
-func (d *errorLocker) IsOnline() bool {
-	return false
-}
-
-func (d *errorLocker) Expired(args dsync.LockArgs) (reply bool, err error) {
-	return false, errors.New("unable to check for lock expiration")
-}
-
 // localLocker implements Dsync.NetLocker
 type localLocker struct {
 	mutex    sync.Mutex