ixgbe: Avoid Tx hang by not allowing more than the number of VFs supported.

ixgbe: Avoid Tx hang by not allowing more than the number of VFs supported.

When DCB is enabled, add checks to ensure creation of number of VF's is
valid based on the traffic classes configured by the device.

Signed-off-by: Usha Ketineni <usha.k.ketineni@intel.com>
Tested-by: Ronald Bynoe <ronald.j.bynoe@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Orabug: 26242766
(cherry picked from commit b5d8acbb8781269cd4e2b986c9b0b884c0ed836a)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>
Reviewed-by: Ethan Zhao <ethan.zhao@oracle.com>