tg3: Don't touch RCB nic addresses

This patch avoids reprogramming the RCB NIC addresses for all 5755 and
later devices.  The address is incorrect for 5717 devices and should be
correct by default for all other affected devices.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>