Acknowledgements
DH thanks Gabriel Nakamura for discussions. This work was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (graduate fellowship to DH). and MCTIC/CNPq grants (proc. 457531/2012-6, 431193/2016-9 and 307689/2014-0 to VDP, and 457447/2012-5 to GO).