Hey Jens,
Please git pull in your 'for-4.7/drivers' the following
branch (based of your 'for-4.7/drivers):
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/for-jens-4.7
which has two fixes for a guest migrating from host that
has multi-queue to one without it (and vice-versa).