Fixed mongoose lying to client about keep alive

If ENABLE_KEEP_ALIVE option set to no and client requests 'Connection: keep-alive'
then mongoose respond with 'Connection: keep-alive' but after that actually closes
the connection. It is happening because of difference beatween suggest_connection_header
and process_new_connection functions.

Author: Vasyl Vavrychuk

src/third_party/mongoose/mongoose.c

@@ -791,7 +791,8 @@ static int should_keep_alive(const struct mg_connection *conn) {
 }
 
 static const char *suggest_connection_header(const struct mg_connection *conn) {
-  return should_keep_alive(conn) ? "keep-alive" : "close";
+  int keep_alive_enabled = !strcmp(conn->ctx->config[ENABLE_KEEP_ALIVE], "yes");
+  return keep_alive_enabled && should_keep_alive(conn) ? "keep-alive" : "close";
 }
 
 static void send_http_error(struct mg_connection *conn, int status,