Overlayfs: turn on redirect directory feature by default

configname: CONFIG_OVERLAY_FS_REDIRECT_DIR

Linux Kernel Configuration
└─>File systems
└─>Overlayfs: turn on redirect directory feature by default
In linux kernel since version 4.1 (release Date: 2015-06-21)  
If this config option is enabled then overlay filesystems will use
redirects when renaming directories by default. In this case it is
still possible to turn off redirects globally with the
"redirect_dir=off" module option or on a filesystem instance basis
with the "redirect_dir=off" mount option.

Note, that redirects are not backward compatible. That is, mounting
an overlay which has redirects on a kernel that doesn't support this
feature will have unexpected results.

If unsure, say N.