nocloud: add static IPv6 network-config support

lib/tiny-cloud/cloud/nocloud/init

@@ -96,6 +96,7 @@ set_network_config_v2() {
 					"iface $target_name" \
 					"$address" >> "$ETC/network/interfaces"
 				gateway="$(get_network_config ethernets/$iface/gateway4)"
+				[ -n "$gateway" ] || gateway="$(get_network_config ethernets/$iface/gateway6)"
 				if [ -n "$gateway" ]; then
 					printf "\tgateway %s\n" "$gateway" >> "$ETC/network/interfaces"
 				fi

tests/tiny-cloud-alpine.test

@@ -15,6 +15,7 @@ init_tests \
 	set_network_config_v2_match_macaddress_set_name_dhcp4 \
 	set_network_config_v2_configures_macifrename_service \
 	set_network_config_v2_static_ipv4 \
+	set_network_config_v2_static_ipv6 \
 	set_network_config_auto \
 	userdata_user_name \
 	userdata_user_homedir \
@@ -215,6 +216,41 @@ set_network_config_v2_static_ipv4_body() {
 		cat etc/resolv.conf
 }
 
+set_network_config_v2_static_ipv6_body() {
+	fake_network_config_nocloud <<-EOF
+		version: 2
+		ethernets:
+		  net0:
+		    match:
+		      macaddress: 52:55:55:1d:2a:0b
+		    set-name: lima0
+		    addresses:
+		      - 2001:db8::10/64
+		    gateway6: 2001:db8::1
+		    nameservers:
+		      addresses:
+		        - 2001:4860:4860::8888
+		        - 2001:4860:4860::8844
+	EOF
+
+	atf_check \
+		-o ignore \
+		-e match:"set_network_interfaces: done" \
+		tiny-cloud boot
+
+	atf_check \
+		-o match:"auto lima0" \
+		-o match:"iface lima0" \
+		-o match:"address 2001:db8::10/64" \
+		-o match:"gateway 2001:db8::1" \
+		cat etc/network/interfaces
+
+	atf_check \
+		-o match:"^nameserver 2001:4860:4860::8888$" \
+		-o match:"^nameserver 2001:4860:4860::8844$" \
+		cat etc/resolv.conf
+}
+
 set_network_config_auto_body() {
 	fake_metadata_nocloud <<-EOF
 		resolv_conf: