Fix all references to config.h

config.h is created in $(top_buildir)/config.h.
Let's make sure all CPPFLAGS add correct -Ipath includes,
and that all code includes the correct file.

Change-Id: Ie9ea38bb009bc715b01cde4d66d181f7bec2e7bd
diff --git a/src/core/Makefile.am b/src/core/Makefile.am
index 2cfb281..9b812ce 100644
--- a/src/core/Makefile.am
+++ b/src/core/Makefile.am
@@ -3,7 +3,7 @@
 # before making any modifications: https://www.gnu.org/software/libtool/manual/html_node/Versioning.html
 LIBVERSION=19:0:0
 
-AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include -I$(top_builddir)
 AM_CFLAGS = -Wall $(TALLOC_CFLAGS) $(PTHREAD_CFLAGS) $(LIBSCTP_CFLAGS) $(LIBMNL_CFLAGS)
 
 if ENABLE_PSEUDOTALLOC