Discovery: Truncate long server names and descriptions

Note that ·SiLA Server Name· and ·SiLA Server Description· might be too long to be encoded as a key/value pair as indicated above. Key/value pairs exceeding the 255 bytes MUST be truncated. Note, that the UTF-8 encoding uses up to 4 bytes per character, depending on the Unicode of the respective character and also consider the bytes used for the key and the equal sign.