dch-gw: Initial commit

The *dch-gw* role, and the corresponding `dch-gw.yml` playbook, apply
all of the necessary configuration to the edge router on my home
network.

roles/dch-gw/files/outside-address.dhcpcd-hook

@@ -0,0 +1,28 @@
+# vim: set ft=sh :
+
+(
+RULESET=/var/lib/dhcpcd/outside-address.ruleset
+
+
+reload_nftables() {
+	systemctl reload nftables
+}
+
+
+write_ruleset() {
+	install -d "${RULESET%/*}"
+	printf 'define outside_address = %s\n' "${new_ip_address}" \
+		> "${RULESET}"
+}
+
+
+if [ -n "${new_ip_address}" ]; then
+	if [ ! -f "${ruleset}" ]; then
+		write_ruleset
+		reload_nftables
+	elif [ "${new_ip_address}" != "${old_ip_address}" ]; then
+		write_ruleset
+		reload_nftables
+	fi
+fi
+)