Fix for fwmark

Evidently, wireguard's (use of) fwmark is not well understood. In short,
it determines which routing table to use for a tunnel's packets.

Adding a fwmark to a roadwarrior client config won't do anything to the
actual packets sent to a peer: Packets do not get marked.

A QRCode with `FwMark = ...` in it is invalid.

FwMark is now excluded from client configs (but is written to the
server config /etc/wireguard/wgX.conf).

Potential breaking change of `WGUI_FORWARD_MARK` to `WGUI_FIREWALL_MARK`

But this has the effect of making users eventually notice that it
probably does not do what they want/think.

See:
https://ro-che.info/articles/2021-02-27-linux-routing

https://casavant.org/2020/10/10/wireguard-fwmark.html

https://www.blinkenlights.ch/ccms/posts/source-based-routing/

templates/clients.html

@@ -70,17 +70,8 @@ Wireguard Clients
             </div>
             <div class="modal-body">
                 <input type="hidden" id="qr_client_id" name="qr_client_id">
-                <a href="" download="" id="qr_code_a">
-                    <img id="qr_code" class="w-100" style="image-rendering: pixelated;" src="" alt="QR code" />
-                </a>
-                <div class="form-group">
-                    <div class="icheck-primary d-inline">
-                        <input type="checkbox" id="qr_include_fwmark" onchange="regenerateQRCode()">
-                        <label for="qr_include_fwmark">
-                            Include FwMark
-                        </label>
-                    </div>
-                </div>
+                <img id="qr_code" class="w-100" style="image-rendering: pixelated;" src="" alt="QR code" />
+                <!-- do not include FwMark in any client configs: it is INVALID. -->
             </div>
         </div>
         <!-- /.modal-content -->
@@ -425,9 +416,7 @@ Wireguard Clients
                 cache: false,
                 method: 'GET',
                 url: '{{.basePath}}/api/client/' + client_id,
-                data: { 
-                    qrCodeIncludeFwMark: include_fwmark
-                },
+                data: JSON.stringify(data),
                 dataType: 'json',
                 contentType: "application/json",
                 success: function (resp) {