Automated cherry pick of #5880: Fix incorrect MTU configurations (#5880) #5926: Ensure MTU is set correctly when WireGuard interface already #5997: Use 65000 MTU upper bound for interfaces in encap mode

Automated cherry pick of #5880: Fix incorrect MTU configurations (#5880) #5926: Ensure MTU is set correctly when WireGuard interface already #5997: Use 65000 MTU upper bound for interfaces in encap mode #308