dnsmasq: add config option for connmark DNS filtering

This adds uci support to configure connmark based DNS filtering.

Signed-off-by: Etan Kissling <etan_kissling@apple.com>
(imported from upstream mailing list
https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q2/015151.html

)
Signed-off-by: Etan Kissling <etan.kissling@gmail.com>

package/network/services/dnsmasq/files/dnsmasq.init

@@ -173,6 +173,10 @@ append_ipset() {
 	xappend "--ipset=$1"
 }
 
+append_connmark_allowlist() {
+	xappend "--connmark-allowlist=$1"
+}
+
 append_interface() {
 	network_get_device ifname "$1" || ifname="$1"
 	xappend "--interface=$ifname"
@@ -938,6 +942,14 @@ dnsmasq_start()
 	config_list_foreach "$cfg" "rev_server" append_rev_server
 	config_list_foreach "$cfg" "address" append_address
 	config_list_foreach "$cfg" "ipset" append_ipset
+
+	local connmark_allowlist_enable
+	config_get connmark_allowlist_enable "$cfg" connmark_allowlist_enable 0
+	[ "$connmark_allowlist_enable" -gt 0 ] && {
+		append_parm "$cfg" "connmark_allowlist_enable" "--connmark-allowlist-enable"
+		config_list_foreach "$cfg" "connmark_allowlist" append_connmark_allowlist
+	}
+
 	[ -n "$BOOT" ] || {
 		config_list_foreach "$cfg" "interface" append_interface
 		config_list_foreach "$cfg" "notinterface" append_notinterface