Very slow network speed using Tinc

[Florent Bautista]

> Do you have jumbograms enabled on your physical network, or are the two VMs
> running on the same machine connected by a virtual network?
>
> That aside, tinc should handle that case, so that is definitely a bug. I'll try
> to find out what is happening.

Yes, for testing purposes, I do this test on 2 VM, on a same host,
connected to a Linux bridge.
But everywhere, MTU is 1500. And that installation worked fine with Tinc
1.0.

Setting 192.168.0.0/24 interface to MTU 1400 in VM worked a few minutes
and then failed (back to 1518 bytes packets).

For the few seconds I could test, performances are better than Tinc 1.0
but not awesome in my tests (179 Mbit/s vs 135 Mbit/s).

Here is my sptps_speed for both VM (aes & pclmulqdq instructions are
available in both VM, host is an i5-2400) :

root at host2:~# sptps_speed
Generating keys for 10 seconds:            580.77 op/s
ECDSA sign for 10 seconds:                 538.36 op/s
ECDSA verify for 10 seconds:               457.77 op/s
ECDH for 10 seconds:                       272.66 op/s
SPTPS/TCP authenticate for 10 seconds:     130.10 op/s
SPTPS/TCP transmit for 10 seconds:           5.01 Gbit/s
SPTPS/UDP authenticate for 10 seconds:     130.27 op/s
SPTPS/UDP transmit for 10 seconds:           5.24 Gbit/s