You need to fully disable it for all interfaces 

<https://support.microsoft.com/en-us/help/929852/guidance-for-configuring-ipv6-in-windows-for-advanced-users>

To configure IPv6, modify the following registry value based on the following
table.

Location:        
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\
Name:             DisabledComponents
Type:             REG_DWORD
Min Value:        0x00
Max Value:        0xFF (IPv6 disabled)