If possible, stop hard-coding magic values that aren't exposed in OpenSSL headers

[nguerrera]

See discussion here: https://github.com/dotnet/corefx/pull/4026/files#r42687456

[eerhardt]

Assigning this to @vijaykota in case he knows of a way to fix this, or to close if there isn't a way.

[vijaykota]

We didn't find any other place for these other than the internal headers so closing this.