net/bnxt: fix error handling in VNIC prepare

net/bnxt: fix error handling in VNIC prepare

Resources should be freed on error conditions. i.e, VNIC and
VNIC context created in HW and memory allocated in
bnxt_vnic_grp_alloc() should be freed.

Added a new function bnxt_vnic_destroy() to do the cleanup.
This lightweight function can be used in flow destroy/flush
path to avoid duplicate code as well.

Fixes: d24610f7bfda ("net/bnxt: allow flow creation when RSS is enabled")
Cc: stable@dpdk.org
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>