The vector number may change during 'dev_start'.
Before enabling a new vector mapping,
it's necessary to disable/unmap the previous setting.
Fixes: fe685de2b1b6 ("igb: fix VF start with PF stopped")
Reported-by: Yong Liu <yong.liu@intel.com>
Signed-off-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: Wenzhuo Lu <wenzhuo.lu@intel.com>