GnuTLS 3.6.5 (TLS 1.3) breaks `tls_session`
- The re-handshake is broken (because unnecessary with TLS 1.3)
- Check if we can be anonymous with 1.2 when the other side is using 1.3
- Crash when handshaking:
#0 0x00007ffff79e5343 in nettle_memxor () at /usr/lib/x86_64-linux-gnu/libnettle.so.6
#1 0x00007ffff7862aa0 in () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#2 0x00007ffff785ef3c in () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#3 0x00007ffff7868cc1 in () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#4 0x00007ffff786ac28 in () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#5 0x00007ffff78ab190 in () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#6 0x00007ffff78ab2be in gnutls_session_key_update () at /usr/lib/x86_64-linux-gnu/libgnutls.so.30
#7 0x0000555555837173 in ring::tls::TlsSession::TlsSessionImpl::handleStateHandshake(ring::tls::TlsSessionState) ()
#8 0x000055555583d9c9 in ring::tls::TlsSession::TlsSessionImpl::process() ()
#9 0x000055555573d59d in ring::ThreadLoop::mainloop(std::thread::id&, std::function<bool ()>, std::function<void ()>, std::function<void ()>) ()
#10 0x000055555573df8a in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (ring::ThreadLoop::*)(std::thread::id&, std::function<bool ()>, std::function<void ()>, std::function<void ()>), ring::ThreadLoop*, std::reference_wrapper<std::thread::id>, std::function<bool ()>, std::function<void ()>, std::function<void ()> > > >::_M_run() ()
#11 0x00007ffff515663f in () at /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007ffff706b164 in start_thread (arg=<optimized out>) at pthread_create.c:486
#13 0x00007ffff4e20def in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95