To workaround a race condition about guest hotplug, c/s
18338:7c10be016e4 disabled do_FLR when we create guest or 'xm
pci-attach' device into guest, so now we actually only do_FLR when a
guest is destroyed or 'xm pci-detach'.
By moving the FLR-related checking/do_FLR logic a little earlier, this
patch re-enables do_FLR in these 2 cases disabled by 18338.
Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>