vmxnet3: Register shutdown handler for device (fwd)

Implement a handler for pci shutdown so that the driver has an
opportunity to make sure that device is quiesced before the PCI
switches to legacy IRQs. This way the possibility of
"screaming interrupt" is avoided.

Acked-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: Shreyas N Bhatewara <sbhatewara@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>