vhost: fix vring addresses not translated

vhost: fix vring addresses not translated

Commit 3ea7052f4b1b ("vhost: postpone rings addresses translation")
moves rings addresses translation at either vring kick or enable
time, depending on whether protocol features are enabled or not.
This is done not interpret ring information as long as the vring
is not fully initialized.

The problem is that with old QEMU versions, like v2.5, the ring
is enabled before addresses are sent, so addresses are never
translated.

This patch fixes the issue by doing the translation in
VHOST_USER_SET_VRING_ADDR handling if ring is already enabled.

Fixes: 3ea7052f4b1b ("vhost: postpone rings addresses translation")

Reported-by: Lei Yao <lei.a.yao@intel.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>