[http] Ignore unrecognised "Connection" header tokens

Some HTTP/2 servers send the header "Connection: upgrade, close".  This
currently causes iPXE to fail due to the unrecognised "upgrade" token.

Fix by ignoring any unrecognised tokens in the "Connection" header.

Reported-by: Ján ONDREJ (SAL) <ondrejj@salstar.sk>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp/httpcore.c

 	if ( value )
 		*value = NULL;
 
-	/* Skip any initial whitespace */
-	while ( isspace ( **line ) )
+	/* Skip any initial whitespace or commas */
+	while ( ( isspace ( **line ) ) || ( **line == ',' ) )
 		(*line)++;
 
 	/* Check for end of line and record token position */
 	/* Scan for end of token */
 	while ( ( c = **line ) ) {
 
-		/* Terminate if we hit an unquoted whitespace */
-		if ( isspace ( c ) && ! quote )
+		/* Terminate if we hit an unquoted whitespace or comma */
+		if ( ( isspace ( c ) || ( c == ',' ) ) && ! quote )
 			break;
 
 		/* Terminate if we hit a closing quote */
  * @ret rc		Return status code
  */
 static int http_parse_connection ( struct http_transaction *http, char *line ) {
+	char *token;
 
 	/* Check for known connection intentions */
-	if ( strcasecmp ( line, "keep-alive" ) == 0 ) {
-		http->response.flags |= HTTP_RESPONSE_KEEPALIVE;
-		return 0;
-	}
-	if ( strcasecmp ( line, "close" ) == 0 ) {
-		http->response.flags &= ~HTTP_RESPONSE_KEEPALIVE;
-		return 0;
+	while ( ( token = http_token ( &line, NULL ) ) ) {
+		if ( strcasecmp ( token, "keep-alive" ) == 0 )
+			http->response.flags |= HTTP_RESPONSE_KEEPALIVE;
+		if ( strcasecmp ( token, "close" ) == 0 )
+			http->response.flags &= ~HTTP_RESPONSE_KEEPALIVE;
 	}
 
-	DBGC ( http, "HTTP %p unrecognised Connection \"%s\"\n", http, line );
-	return -ENOTSUP_CONNECTION;
+	return 0;
 }
 
 /** HTTP "Connection" header */