build: fix dist tarball

automake file lists haven't quite kept up with recent changes, time to
fix them up so the dist tarball actually works...

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/Makefile.am b/zebra/Makefile.am
index 266812f..96f7bef 100644
--- a/zebra/Makefile.am
+++ b/zebra/Makefile.am
@@ -42,7 +42,8 @@
 
 noinst_HEADERS = \
 	connected.h ioctl.h rib.h rt.h zserv.h redistribute.h debug.h rtadv.h \
-	interface.h ipforward.h irdp.h router-id.h kernel_socket.h
+	interface.h ipforward.h irdp.h router-id.h kernel_socket.h \
+	rt_netlink.h zebra_fpm.h zebra_fpm_private.h
 
 zebra_LDADD = $(otherobj) ../lib/libzebra.la $(LIBCAP) $(LIB_IPV6)