net/bnxt: fix possible stack smashing

net/bnxt: fix possible stack smashing

We see a stack smashing as a result of defensive code missing. Once the
nb_pkts is less than RTE_BNXT_DESCS_PER_LOOP, it will be modified to
zero after doing a floor align, and we can not exit the following
receiving packets loop. And the buffers will be overwrite, then the
stack frame was ruined.

Fix the problem by adding defensive code, once the nb_pkts is zero, just
directly return with no packets.

Fixes: bc4a000f2f53 ("net/bnxt: implement SSE vector mode")
Cc: stable@dpdk.org
Signed-off-by: Linsi Yuan <yuanlinsi01@baidu.com>
Signed-off-by: Dongsheng Rong <rongdongsheng@baidu.com>
Acked-by: Lance Richardson <lance.richardson@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>