luci-proto-wireguard: add support for fwmark option

Adds support for the fwmark option.

FwMark is a 32-bit fwmark for outgoing packets.
If set to 0 or "off", this option is disabled.

Signed-off-by: Dan Luedtke <mail@danrl.com>

modules/luci-base/luasrc/cbi/datatypes.lua

@@ -283,6 +283,14 @@ function hexstring(val)
 	return false
 end
 
+function hex(val, maxbytes)
+	maxbytes = tonumber(maxbytes)
+	if val and maxbytes ~= nil then
+		return ((val:match("^0x[a-fA-F0-9]+$") ~= nil) and (#val <= 2 + maxbytes * 2))
+	end
+	return false
+end
+
 function base64(val)
 	if val then
 		return (val:match("^[a-zA-Z0-9/+]+=?=?$") ~= nil) and (math.fmod(#val, 4) == 0)

protocols/luci-proto-wireguard/luasrc/model/cbi/admin_network/proto_wireguard.lua

@@ -85,6 +85,18 @@ preshared_key.datatype = "and(base64,rangelength(44, 44))"
 preshared_key.optional = true
 
 
+fwmark = section:taboption(
+  "advanced",
+  Value,
+  "fwmark",
+  translate("Firewall Mark"),
+  translate("Optional. 32-bit mark for outgoing encrypted packets. " ..
+            "Enter value in hex, starting with <code>0x</code>.")
+)
+fwmark.datatype = "hex(4)"
+fwmark.optional = true
+
+
 -- peers -----------------------------------------------------------------------
 
 peers = map:section(