The patch comes from OpenEmbedded

--- ppp-2.4.3/pppd/Makefile.linux.orig	2005-10-28 21:07:40.396359250 +0100
+++ ppp-2.4.3/pppd/Makefile.linux	2005-10-28 21:07:54.217223000 +0100
@@ -62,7 +62,7 @@
 
 HAS_SHADOW=y
 #USE_PAM=y
-#HAVE_INET6=y
+HAVE_INET6=y
 
 # Enable plugins
 PLUGIN=y
