Always close connection if a BAD REQUEST (400) is detected

[u413-284-si]

extracted from RFC 9112: "When a server listening only for HTTP request messages, or processing what appears from the start-line to be an HTTP request message, receives a sequence of octets that does not match the HTTP-message grammar aside from the robustness exceptions listed above, the server SHOULD respond with a 400 (Bad Request) response and close the connection."

TO DOs:

• remove boolean in HTTPRequest struct
• implement closing of connection by the server