[TG3]: Use status tag to check for new events

Use the status tag to determine if there are new events in
tg3_interrupt_tagged(). We discussed about this a while ago with Grant
Grundler and DaveM. This scheme makes it unnecessary to clear the
updated bit in the status block when using tagged mode, and only
a simple comparison is needed to determine if there are new events.

The tp->lock around netif_rx_complete() and tg3_restart_ints() is also
removed. It is unnecessary with DaveM's new locking scheme.

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