build: get rid of INCLUDES, use AM_CPPFLAGS

INCLUDES in configure.ac was not used at all, and INCLUDES in
Makefile.am is supposed to be AM_CPPFLAGS these days.

Reduces warnings spewed during bootstrap/autoreconf.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Acked-by: Greg Troxel <gdt@ir.bbn.com>
Acked-by: Feng Lu <lu.feng@6wind.com>
Acked-by: Paul Jakma <paul@jakma.org>
diff --git a/ripngd/Makefile.am b/ripngd/Makefile.am
index de5beba..9bd14ba 100644
--- a/ripngd/Makefile.am
+++ b/ripngd/Makefile.am
@@ -1,6 +1,6 @@
 ## Process this file with automake to produce Makefile.in.
 
-INCLUDES = @INCLUDES@ -I.. -I$(top_srcdir) -I$(top_srcdir)/lib -I$(top_builddir)/lib
+AM_CPPFLAGS = -I.. -I$(top_srcdir) -I$(top_srcdir)/lib -I$(top_builddir)/lib
 DEFS = @DEFS@ -DSYSCONFDIR=\"$(sysconfdir)/\"
 INSTALL_SDATA=@INSTALL@ -m 600