The tun driver allocates skb's to hold data from user and then passes
the data into the network stack as received data. Most network devices
allocate the receive skb with routines like dev_alloc_skb() that reserves
additional space for use by network protocol stack but tun does not.
Because of the lack of padding, when the packet is passed through bridge
netfilter a new skb has to be allocated.
Signed-off-by: Stephen Hemminger <email@example.com>
Signed-off-by: David S. Miller <firstname.lastname@example.org>
(cherry picked from commit a504b86e718a425ea4a34e2f95b5cf0545ddfd8d)