The fw_l2_filter_id for a ntuple filter is needed only for the lifetime
of the ntuple filter. Once the filter is free, reset the field.
The associated l2_filter will be freed as a part of its own cleanup.
Fixes: 5ef3b79fdfe6 ("net/bnxt: support flow filter ops")
Cc: stable@dpdk.org
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>