extension: net: Refactor, fix and improve network extensions

- Rename extensions with "net-*" prefix
- Put the extensions into their own folder
- Split off time sync packages into their own extensions to be able to be used separately
- Put their config files into directories instead of using inline `cat <<- EOF >`
- Move some other NetworkManager related stuff into the extension
- Remove unneeded steps
- Install iproute2 by default on all images (for the `ip` command)

config/cli/common/main/packages

@@ -13,9 +13,10 @@ fake-hwclock
 fdisk
 figlet
 htop
-init
 inetutils-ping
+init
 initramfs-tools
+iproute2
 iw
 jq
 logrotate