vhost: fix crash on reconnect

vhost: fix crash on reconnect

When the vhost-user frontend like Virtio-user tries to
reconnect to the restarted Vhost backend, the Vhost backend
segfaults when multiqueue is enabled.

This is caused by VHOST_USER_GET_VRING_BASE being called for
a virtqueue that has not been created before, causing a NULL
pointer dereferencing.

This patch adds the VHOST_USER_GET_VRING_BASE requests to
the list of requests that trigger queue pair allocations.

Fixes: 160cbc815b41 ("vhost: remove a hack on queue allocation")
Cc: stable@dpdk.org
Reported-by: Yinan Wang <yinan.wang@intel.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Yinan Wang <yinan.wang@intel.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>