Trying to access xstats_names after "if (xstats_names == NULL)" is
obviously wrong, which would result to a crash while running "show
port xstats 0" in testpmd with virtio PMD.
The fix is straightforward; just reverse the check.
Fixes: baf91c395b18 ("net/virtio: fetch extended statistics with integer ids")
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
7e1eb993f2