convert / build: add networking support through network-manager flag

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

templates/alpine.Dockerfile

@@ -21,3 +21,11 @@ RUN for s in devfs dmesg hwdrivers mdev; do rc-update add $s sysinit; done
 
 RUN echo "root:{{- if .Password}}{{ .Password}}{{- else}}root{{- end}}" | chpasswd
 
+{{ if eq .NetworkManager "ifupdown"}}
+RUN apk add --no-cache ifupdown-ng
+RUN mkdir -p /etc/network && printf '\
+auto eth0\n\
+allow-hotplug eth0\n\
+iface eth0 inet dhcp\n\
+' > /etc/network/interfaces
+{{ end }}