site: add kmod-nlmon

For debugging issues related to netlink on the routers, it is very
useful to inspect what is happening via netlink in the kernel. Add
kmod-nlmon for that.

site.mk

@@ -33,6 +33,7 @@ GLUON_SITE_PACKAGES := \
 	respondd \
 	respondd-module-airtime \
 	gluon-radv-filterd \
+	kmod-nlmon \
 
 
 #  activate for wifi fallback later in production