bnx2x: ETS changes

Fix a problem when new traffic class is created with 0% BW, the ETS is not conforming.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>