[TG3]: Add some missing netif_running() checks

Add missing netif_running() checks in tg3's dev->set_multicast_list()
and dev->set_mac_address(). If not netif_running(), these 2 calls can
simply return 0 after storing the new settings if required.

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