libwebsockets

Pass HTTP reject error code returned by server to client

AG: added changelog and documentation comment

Signed-off-by: Gadkari Mugdha <mugdha.gadkari@siemens.com>
Reviewed-by: Roger Meier <r.meier@siemens.com>

HTTP reject error code returned by server during HTTP handshake is extracted and sent to the client application.
With this fix, the Connection error callback will include the HTTP reject status code and response frame received from server. This string passed in Connection error callback can be read or ignored by client application based on client application requirement