Bug#747098: can't ssh over OpenConnect from client running sid

[Mike Kupfer <m.kupfer@acm.org>]

I've been seeing an issue that is very similar to what is described in
747098 and 612607, where there's a hang after

  ...
  debug1: kex: server->client aes128-ctr umac-64@openssh.com zlib@openssh.com
  debug1: kex: client->server aes128-ctr umac-64@openssh.com zlib@openssh.com
  debug1: sending SSH2_MSG_KEX_ECDH_INIT
  debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

This only happens when connecting through an OpenConnect tunnel; ssh
works fine when I'm not using VPN.

Specifying a cipher didn't help, but lowering the MTU for the VPN tunnel
from 1500 to 1300 fixed things.

# ip li set mtu 1300 dev vpn0

mike