Make the SSL plugin work within the Linux based Docker container

[matyasmarkovics]

No description provided.

[z3APA3A]

Can you change few things for pull to be accepted pls:

1. for _set_errno add

#else
errno = ...

Or replace this fix with

#ifndef _set_errno
#define _set_errno(x) (errno = x)
#endif

in #ifndef _WIN32 section of proxy.h

2. For no shared cipher - I'm not sure it's a best fix, it's a bit strange. May be first commenter on stackoverflow is right and limiting the TLS version is actually required.

[matyasmarkovics]

Thanks @z3APA3A, I've applied y our comment on _set_errno. I've only found #ifdef _WIN32, so I've added an #else to it. Hope that's fine.

After researching the no-shared-cipher issue more, I've decided to exclude it.
I got this message: error:142090C1:SSL routines:tls_early_post_process_client_hello:no shared cipher.
Despite the message the request goes through (maybe on a 2nd attempt).

I've tried the suggested change: const long flags = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_COMPRESSION;...., but it didn't make a difference. Maybe the issue is with my certificates.

Anyway, this PR makes the SSL-plugin functional for me within the docker. Thanks for the feedback!

[matyasmarkovics]

Any remaining issues you see on this @z3APA3A ?