igb: Check if subordinate VFs are assigned to virtual machines

Kvm and the Xen pci-back driver will set a flag in the virtual function
pci device dev_flags when the VF is assigned to a guest VM.  Before
destroying subordinate VFs check to see if the flag is set and if so
skip the call to pci_disable_sriov() to avoid system crashes.

Copy the maintainer for the Xen pci-back driver.  Also CC'ing
maintainers of all drivers found to call pci_disable_sriov().

V2 - Fix  uninitialized variable warning

Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Christian Benvenuti <benve@cisco.com>
Cc: Sathya Perla <sathya.perla@emulex.com>
Cc: Dimitris Michailidis <dm@chelsio.com>
Cc: Jon Mason <jdmason@kudzu.us>
Cc: James Smart <james.smart@emulex.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb.h

@@ -72,6 +72,8 @@ struct igb_adapter;
 #define IGB_MAX_VF_MC_ENTRIES              30
 #define IGB_MAX_VF_FUNCTIONS               8
 #define IGB_MAX_VFTA_ENTRIES               128
+#define IGB_82576_VF_DEV_ID                0x10CA
+#define IGB_I350_VF_DEV_ID                 0x1520
 
 struct vf_data_storage {
 	unsigned char vf_mac_addresses[ETH_ALEN];
@@ -83,6 +85,7 @@ struct vf_data_storage {
 	u16 pf_vlan; /* When set, guest VLAN config not allowed. */
 	u16 pf_qos;
 	u16 tx_rate;
+	struct pci_dev *vfdev;
 };
 
 #define IGB_VF_FLAG_CTS            0x00000001 /* VF is clear to send data */