Report security level instead of key size for 3DES

[tyll]

3DES is currently reported with 168 bits because of its key size, but the security level is only 112 bits:
https://www.ietf.org/rfc/rfc2246.txt (page 57) - IMHO it would be better to report the security level.

[phibos]

The information about the security level should be added to the tls cipher suite registry in the FlexTLS Python package. I have created a new issue DinoTools/python-flextls#15 to fix it.