tg3: Return flowctrl config through ethtool

This patch changes the driver to return the flow control configuration
rather than the flow control status through the ETHTOOL_GPAUSEPARAM
ioctl.

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