site: re-add gluon-ffbsnext-wireguard

An older version-bump mistakenly removed the gluon-wireguard package,
thinking it was an upstream package. We have no renamed it according to
our internal naming scheme, re-add it as gluon-ffbsnext-wireguard.

site.mk

@@ -25,6 +25,7 @@ GLUON_SITE_PACKAGES := \
 	gluon-ffbsnext-debugrsyslog \
 	gluon-ffbsnext-nextnode \
 	gluon-ffbsnext-info-pull \
+	gluon-ffbsnext-wireguard \
 	usign \
 	-gluon-ebtables-limit-arp \
 	gluon-ebtables-filter-ra-dhcp \