Any executable script *.sh placed in this directory will be run by ifdown-post
after a static network interface goes down, just like /sbin/ifdown-local.

However, unlike that script, no arguments are passed and the script inherits
the caller's private environment.  This makes it simpler to access relevant
variables (such as $DEVICE or $REALDEVICE), but also exposes some
implementation details.  Be careful about which global variables you rely on.
