skeleton/S40network: tweak for debian ifupdown

Make the S40network script create the /run/network directory for the
debian variant of ifupdown which uses it as a lock directory.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Tested-by: Karoly Kasza <kaszak@gmail.com>
Reviewed-by: Karoly Kasza <kaszak@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>