igb: Unpair the queues when changing the number of queues

igb: Unpair the queues when changing the number of queues

By the commit 72ddef0506da ("igb: Fix oops caused by missing queue
pairing"), the IGB_FLAG_QUEUE_PAIRS flag can now be set when changing the
number of queues by "ethtool -L", but it is never cleared unless the igb
driver is reloaded.
This patch clears it if queue pairing becomes unnecessary as a result of
"ethtool -L".

Signed-off-by: Shota Suzuki <suzuki_shota_t3@lab.ntt.co.jp>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 37a5d163fb447b39f7960d0534de30e88ad395bb)

Orabug: 26325580

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>