In Windows 2008, I can disable this on Remote Desktop Session Host Configuration but in Server 2012 is not active if you don’t enable RDP roles

You have two ways to do it:

You may set this via group policy, for example, in the server’s local policy using gpedit.msc:

Computer Configuration\ Administrative Templates\ Windows Components\ Remote Desktop Services\ Remote Desktop Session Host\ Connections\
Restrict Remote Desktop Services users to a single Remote Desktop Services session Disabled
Or you could edit the server’s registry:

HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server
fSingleSessionPerUser REG_DWORD 0x00000000