package/libnet: add LIBNET_CONFIG_SCRIPTS

Set LIBNET_CONFIG_SCRIPTS to libnet-config to fix a build failure with
syslog-ng and libnet in version 1.2 due to -L$(libdir) which has been
added with
https://github.com/libnet/libnet/commit/6859d1f198f97aad129c54fcd156700a9178204e

Fixes:
 - http://autobuild.buildroot.org/results/45e517401d14e304e9c6c990f1b4ead92c850ba2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/libnet/libnet.mk

@@ -13,5 +13,6 @@ LIBNET_CONF_OPTS = libnet_cv_have_packet_socket=yes
 LIBNET_LICENSE = BSD-2-Clause, BSD-3-Clause
 LIBNET_LICENSE_FILES = LICENSE
 LIBNET_CPE_ID_VENDOR = libnet_project
+LIBNET_CONFIG_SCRIPTS = libnet-config
 
 $(eval $(autotools-package))