net/ena: fix crash with unsupported device argument

net/ena: fix crash with unsupported device argument

As the documentation of rte_kvargs_parse() states, the valid_keys
argument must be NULL terminated. Lack of this feature may cause
segmentation fault if the passed devarg will be different then the
supported value.

Fixes: 8a7a73f26cc9 ("net/ena: support large LLQ headers")
Cc: stable@dpdk.org
Signed-off-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Igor Chauskin <igorch@amazon.com>
Reviewed-by: Shay Agroskin <shayagr@amazon.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>