bnx2x: Fix SFP+ current leakage

Per measurements, the SFP+ suffered from small current leakage in two cases:
 - When no module was plugged and TX laser was disabled. The fix was to enable
   it, and when module is plugged in, check if it needs to be disabled.
 - When over-current event occurs due to invalid SFP+ module, the HW basically
   shuts down the current for this module, but the SW needs to complete this
   by issuing a power down via a GPIO.

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>