Adding changeable MTU to VPN interface

[malcolmdavis224]

Is your feature request related to a problem? Please describe. My specific Wireguard VPN client (Surfshark) uses a different MTU than the default provided by the router (1420 default when SS uses 1350). The 1420 MTU doesn’t allow for Wireguard to work, I had to manually SSH into the router and change the Wireguard client MTU to 1350. It works afterwards. Describe the solution you'd like Add a field under each VPN section (OpenVPN, L2TP, Wireguard) that allows for a manual MTU change from the default value of 1420.

Describe alternatives you've considered N/A

Additional context N/A