Add support for --enable-exampledir to specify where to place example
files, defaulting to sysconfdir (matching previous behavior).

This is needed to support (cleanly) NetBSD pkgsrc, which requires that
example config files go in $(prefix)/share/examples/pkgname, rather
than in $(prefix)/etc/pkgname.
diff --git a/ripngd/Makefile.am b/ripngd/Makefile.am
index 2e6c677..ecd71f8 100644
--- a/ripngd/Makefile.am
+++ b/ripngd/Makefile.am
@@ -19,5 +19,6 @@
 
 ripngd_LDADD = -L../lib -lzebra @LIBCAP@
 
-dist_sysconf_DATA = ripngd.conf.sample
+examplesdir = $(exampledir)
+dist_examples_DATA = ripngd.conf.sample