[TG3]: Call netif_carrier_off() during phy reset

Add netif_carrier_off() call during tg3_phy_reset(). This is needed
to properly track the netif_carrier state in cases where we do a
PHY reset with interrupts disabled. The SerDes code will not run
properly if the netif_carrier state is wrong.

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