net/netvsc: fix hot adding multiple VF PCI devices

net/netvsc: fix hot adding multiple VF PCI devices

This patch fixes two issues with hot removing/adding a VF PCI device:
1. The original device argument is lost when it's hot added
2. If there are multiple VFs hot adding at the same time, some of the
   VFs may not get added successfully because only one single VF status
   is stored in the netvsc.

Fix these by storing the original device arguments and maintain a list
of hot add contexts to deal with multiple VF devices.

Fixes: a2a23a794b ("net/netvsc: support VF device hot add/remove")
Cc: stable@dpdk.org
Signed-off-by: Long Li <longli@microsoft.com>