Add keylog callback support (added in openssl 1.1.1)

[schveiguy]

Please review, trying to access some undeclared prototypes. I'm not sure if I did this right.

C headers are defined here:

openssl/C/openssl-1.1.1p/ssl.h

Lines 912 to 929 in 836c22a

	/*
	* A callback for logging out TLS key material. This callback should log out
	* |line| followed by a newline.
	*/
	typedef void (*SSL_CTX_keylog_cb_func)(const SSL *ssl, const char *line);
	/*
	* SSL_CTX_set_keylog_callback configures a callback to log key material. This
	* is intended for debugging use with tools like Wireshark. The cb function
	* should log line followed by a newline.
	*/
	void SSL_CTX_set_keylog_callback(SSL_CTX *ctx, SSL_CTX_keylog_cb_func cb);
	/*
	* SSL_CTX_get_keylog_callback returns the callback configured by
	* SSL_CTX_set_keylog_callback.
	*/
	SSL_CTX_keylog_cb_func SSL_CTX_get_keylog_callback(const SSL_CTX *ctx);

[schveiguy]

ping @Geod24

[Geod24]

Looks right