net/bnxt: fix xstats names query overrun

net/bnxt: fix xstats names query overrun

When the xstats_names parameter to rte_eth_xstats_get_names()
is non-NULL and the size parameter is less than the required
number of entries, the driver must return the required size
without modifying (and over-running) the caller's xstats_names
array.

Update bnxt_dev_xstats_get_names_op() in accordance with this
requirement.

Fixes: bfb9c2260be2 ("net/bnxt: support xstats get/reset")
Cc: stable@dpdk.org
Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>