changed the config dir from network.d to netctl

netctl uses /etc/netctl/ to store it's config files
/etc/network.d/ is legacy and shouldn't be used
changed net-interface program to ip from ifconfig

ifconfig is in package net-tools and is around to
prevent scripts from breaking it should be avoided
see
https://bbs.archlinux.org/viewtopic.php?pid=945602
https://www.archlinux.org/news/deprecation-of-net-tools/

re line 254; we're disconnecting from a network
there's no reason to leave the interface up and
netctl expects it to be down so we'll just leave
it down.
prompt the user to sudo or exit