It has been reported that under certain heavy traffic conditions in MSI-X
mode, the driver can lose an MSI-X vector causing all packets in the
associated rx/tx ring pair to be dropped.  The problem is caused by
the chip dropping the write to unmask the MSI-X vector by the kernel
(when migrating the IRQ for example).

This can be prevented by increasing the GRC timeout value for these
register read and write operations.

Thanks to Dell for helping us debug this problem.
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>