CVE request: kernel: igb panics when receiving tag vlan packet

[Eugene Teo <eugene () redhat com>]

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 vlan_gro_receive is only used if vlans have been registered 
to the adapter structure.

Reference:
https://bugzilla.redhat.com/show_bug.cgi?id=660188
https://bugzilla.kernel.org/show_bug.cgi?id=15582

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

Thanks, Eugene