tg3: Allow phylib flowctrl changes anytime

This patch loosens the restriction that the phylib interface must be up
and running to change the flow control parameters.

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