bnx2x: 1G sfp+ module handling

Automatically lower requested link speed to 1G in case 1G SFP+
module is detected.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Yaniv Rosner <yaniv.rosner@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>