FreeBSD 10.x/11 domu network issue

[smj%ma.sdf.org@localhost]

I've posted to freebsd-xen concerning an issue I've seen with the network 
running a FreeBSD 10.x or 11 DOMU under a NetBSD 7 (xen4.5) DOM0.  There
is a thought over there than it isn't there netfront but rather NetBSD's
netback causing this problem.

What is odd is that I can get through a network install without any issues
for both installs of 10.3 and 11.0, but the system I bring up is unable to
talk on the network successfully.  The DOMU responds to pings (to and from)
but trying something like an ssh in or out results in:

debug1: Local version string SSH-2.0-OpenSSH_6.8 NetBSD_Secure_Shell-20150403
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2 FreeBSD-20160310
debug1: match: OpenSSH_7.2 FreeBSD-20160310 pat OpenSSH* compat 0x04000000
debug1: Remote is NON-HPN aware
debug1: mac 0x0, -1 -1
debug1: SSH2_MSG_KEXINIT sent
Bad packet length 168430090.
debug1: mac 0x0, -1 -1
ssh_dispatch_run_fatal: message authentication code incorrect

In my config:

vif = [ 'mac=00:16:3e:00:00:30,bridge=bridge0, type=ioemu' ]

FreeBSD uses the xn driver (at least on the production domu that is created
after the successful net install).

Other domu: (Plan9, Centos 7, Debian (jess), NetBSD 7, OpenBSD 5.9 and Multics)
are talking on the network well.

The MAC is valid and is not conflicting with anything on the network.