Allow setting additional openssl CTX options from client applications (#600)

[mazer1310]

Problem

OpenSSL 3.x behavior with respect to abruptly closed sockets when connecting to the WebSocket server results in spurious error messages. The workaround as described in openssl/openssl#22690 is to call SSL_set_options (or SSL_CTX_set_options with option SSL_OP_IGNORE_UNEXPECTED_EOF. However, IXWebSockets does not expose the ability to do so from client applications. (fixes #600)

Fix

Add int additional_openssl_ctx_options to ix::SocketTLSOptions

• Defaults to 0, so the behavior is unchanged for existing applications.
• clients can set it to a desired value to include the options in the SSL_CTX_set_options calls during client and server socket handshakes
• adds a call to SSL_CTX_set_options during SocketOpenSSL::handleTLSOptions to handle the client handshake
• appends the options to the existing SSL_CTX_set_options call in SocketOpenSSL::accept to handle the server handshake

Verification

Built the library on Linux RH8 and tested our application with and without setting SocketTLSOptions::additional_openssl_ctx_options to SSL_OP_IGNORE_UNEXPECTED_EOF and confirmed that the application functions in both modes, but with the additional option the spurious error messages are squelched.