bnx2x: Clean the sp rtnl task upon unload

While unloading, bnx2x needs to clean the sp_rtnl_state to prevent
configuration made before the unload to be applied afterwards with
stale values.

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>