net/bnxt: check for error conditions in Tx path

The HW can have limits on the minimum packet size it can support,
or the maximum number of segments it can support. Check for such
possibilities. Also check if we are going to have a 0 length buffer.

Fixes: 6eb3cc2294fd ("net/bnxt: add initial Tx code")
Cc: stable@dpdk.org
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>