page-server: wait when a socket will be closed only if it isn't external

External socket can be used for other purpose.
Reported-by: Adrian Reber <adrian@lisas.de>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Adrian Reber <adrian@lisas.de>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

page-xfer.c

@@ -257,7 +257,7 @@ static int page_server_serve(int sk)
 		ret = -1;
 	}
 
-	if (ret == 0) {
+	if (ret == 0 && opts.ps_socket == -1) {
 		char c;
 
 		/*