secnet: Avoid netlink crash; MTU, frag. and security fixes

[Ian Jackson]

Ian Jackson writes ("[PATCH 0/3] netlink: Avoid crash with clientless netlink"):
> Barring objections I intend to include this in a secnet 0.3.1 release
> soonish.
> 
>  1/3 netlink: Break out netlink_client_deliver
>  2/3 netlink: Avoid crash with clientless netlink
>  3/3 netlink: Remove a newline from p-t-p startup message

Ian Jackson writes ("[PATCH 00/21] secnet: MTU and security fixes, fragmentation, etc."):
> This series:
>  Fixes some (not catastrophic) packet size & ICMP vulnerabilities
>  Implements IP fragmentation (and the sending of ICMP Frag Needed)
>  Negotiates inter-site link MTU with peer secnets
>  Fixes a few other bugs I came across
>  Makes some code cleanups which are necessary to enable the above

In the absence of comments I have pushed these series to master, and
also deployed the result on chiark.  It all seems to work.

I intend to make a beta release soonish.

Ian.