tg3: Avoid null pointer dereference in tg3_interrupt in netconsole mode

tg3: Avoid null pointer dereference in tg3_interrupt in netconsole mode

commit 9c13cb8bb477a83b9a3c9e5a5478a4e21294a760 upstream.

When netconsole is enabled, logging messages generated during tg3_open
can result in a null pointer dereference for the uninitialized tg3
status block. Use the irq_sync flag to disable polling in the early
stages. irq_sync is cleared when the driver is enabling interrupts after
all initialization is completed.

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[PG: drivers/net/ethernet/broadcom/tg3.c --> drivers/net/tg3.c in .34]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>