bnxt_en: Refactor L2 filter alloc/free firmware commands.

Refactor the L2 filter alloc/free logic so that these filters can be
added/deleted by the user.

The bp->ntp_fltr_bmap allocated size is also increased to allow enough
IDs for L2 filters.

Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>