ethdev: fix xstats get by id APIs

ethdev: fix xstats get by id APIs

xstats _by_id() APIs are broken because ids known by user sent directly
to the PMDs.

ethdev xstat get by id APIs:
rte_eth_xstats_get_names_by_id() and rte_eth_xstats_get_by_id()
work on ids calculated as "basic stats + extended stats"

When an application asking for id less than "basic stats count", it is
indeed asking basic stats not extended stats.

The dev_ops PMDs implements work on extended stats ids.

This patch adds a check if all requested stats are xstats and if so
converts ids to xstats ids before passing them to PMDs.

This conversion wasn't required before commit 8c49d5f1c219, because
_by_id dev_ops were always used to get whole stats via NULL ids.

Fixes: 8c49d5f1c219 ("ethdev: rework xstats retrieve by id")
Cc: stable@dpdk.org
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Reviewed-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Tested-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Acked-by: Thomas Monjalon <thomas@monjalon.net>