net: fix DCB setstate to return success/failure

Data Center Bridging (DCB) had no way to know if setstate had failed in the
driver.  This patch enables dcb netlink code to handle the status for the DCB
setstate interface.  Likewise it allows the driver to return a failed status
if MSI-X isn't enabled.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Eric W Multanen <eric.w.multanen@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>