decnet: Disable auto-loading as mitigation against local exploits

decnet: Disable auto-loading as mitigation against local exploits

Recent review has revealed several bugs in obscure protocol
implementations that can be exploited by local users for denial of
service or privilege escalation.  We can mitigate the effect of any
remaining vulnerabilities in such protocols by preventing unprivileged
users from loading the modules, so that they are only exploitable on
systems where the administrator has chosen to load the protocol.

The 'decnet' protocol is unmaintained and of mostly historical
interest, and the user-space support package 'dnet-common' loads the
module explicitly.  Therefore disable auto-loading.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic debian
Gbp-Pq: Name decnet-Disable-auto-loading-as-mitigation-against-lo.patch