gro: reset vlan_tci on reuse

gro: reset vlan_tci on reuse

This one liner is part of upstream
commit 3701e51382a026cba10c60b03efabe534fba4ca4
Author: Jesse Gross <jesse@nicira.com>

    vlan: Centralize handling of hardware acceleration.

The bulk of that commit is a rework of the hardware assisted vlan tagging
driver interface, and as such doesn't classify for -stable inclusion. The fix
that is needed is a part of that commit but can work independently of the
rest.

This patch can avoid panics on the 2.6.32.y -stable kernels and is in the same
spirit as mainline commits
66c46d7 gro: Reset dev pointer on reuse
6d152e2 gro: reset skb_iif on reuse
which are already in -stable.

For drivers using the vlan_gro_frags() interface, a packet with an invalid tci
leads to GRO_DROP and napi_reuse_skb(). The skb has to be sanitized before
being reused or we may send an skb with an invalid vlan_tci field up the stack
where it is not expected.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Cc: Jesse Gross <jesse@nicira.com>
Acked-by: David S. Miller <davem@davemloft.net>