Add support for EAP-MSCHAPv2

[enaess]

There is an implementation available here. I also created a branch for this fix here: https://github.com/enaess/ppp-eap-mschapv2

https://w3logistics.com/blog/archives/438-EAP-MSCHAPv2-for-pppd-2-4-7.html

[Neustradamus]

EDIT: @enaess, @tisj: Please look @paulusmack comments :)

• https://github.com/paulusmack/ppp/pull/139 -> https://github.com/paulusmack/ppp/pull/175 -> https://github.com/paulusmack/ppp/pull/211
• https://github.com/paulusmack/ppp/pull/177

[enaess]

Okay, let me do this again against the latest tip of master branch.

[enaess]

@Neustradamus @paulusmack

Added new pull request that contains all the changes to add EAP-MSCHAPv2.

Please have a look at #211