If igb's SR-IOV and promiscuous mode are enabled and the interface receives a tag VLAN packet, this will result in a null pointer dereference. To fix this, we will backport upstream commit 31b24b95 to ensure that vlangroreceive is only used if vlans have been registered to the adapter structure.

[ This fixes bugzilla entry 15582 -Eric Dumazet]

It matters if CONFIGPCIIOV is enabled, e.g. grep -ir SRIOV drivers/net/igb/.

Upstream commit: http://git.kernel.org/linus/31b24b95

References: https://bugzilla.kernel.org/showbug.cgi?id=15582