Add TLSv1.3 support

Actually, TLSv1.3 will be enabled without this change if xrdp is compiled
with OpenSSL or alternatives which support TLSv1.3. This commit makes to
enable or disable TLSv1.3 explicitly.  Also, this commit adds a log
"TLSv1.3 enabled by config, but not supported by system OpenSSL". if
xrdp installation doesn't support TLSv1.3. It should be user-friendly.

common/ssl_calls.c

@@ -1004,8 +1004,23 @@ ssl_get_protocols_from_string(const char *str, long *ssl_protocols)
 #endif
 #if defined(SSL_OP_NO_TLSv1_2)
     protocols |= SSL_OP_NO_TLSv1_2;
+#endif
+#if defined(SSL_OP_NO_TLSv1_3)
+    protocols |= SSL_OP_NO_TLSv1_3;
 #endif
     bad_protocols = protocols;
+    if (g_pos(str, ",TLSv1.3,") >= 0)
+    {
+#if defined(SSL_OP_NO_TLSv1_3)
+        log_message(LOG_LEVEL_DEBUG, "TLSv1.3 enabled");
+        protocols &= ~SSL_OP_NO_TLSv1_3;
+#else
+        log_message(LOG_LEVEL_WARNING,
+                    "TLSv1.3 enabled by config, "
+                    "but not supported by system OpenSSL");
+        rv |= (1 << 6);
+#endif
+    }
     if (g_pos(str, ",TLSv1.2,") >= 0)
     {
 #if defined(SSL_OP_NO_TLSv1_2)