examples/vhost: fix corrupted vdev tailq list

examples/vhost: fix corrupted vdev tailq list

There are two tailq lists, one for logging all vhost devices, another
one for logging vhost devices distributed on a specific core. However,
there is just one tailq entry, named "next", to chain the two list,
which is wrong and could result to a corrupted tailq list, that the
tailq list might always be non-empty: the entry is still there even
after you have invoked TAILQ_REMOVE several times.

Fix it by introducing two tailq entries, one for each list.

Fixes: 45657a5c6861 ("examples/vhost: use tailq to link vhost devices")

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>