net/ixgbe: fix link status inconsistencies

net/ixgbe: fix link status inconsistencies

Setting LINK UP or LINK DOWN is divided into two parts, with
the main task done in a separate thread, which can take up
to 9 seconds. If cancel the thread in execution, may cause state
inconsistencies. Therefore, must wait for the previous setting
to exit normally before setting the new state.

Note: before using threads, use alarm to handle main tasks.
When canceling alarm, the execution of alarm will not be interrupted.

Fixes: 819d0d1d57f1 ("net/ixgbe: fix blocking system events")
Cc: stable@dpdk.org
Signed-off-by: Tao Zhu <taox.zhu@intel.com>
Acked-by: Xiaolong Ye <xiaolong.ye@intel.com>
Tested-by: Yu Jiang <yux.jiang@intel.com>