Clear IFF_XMIT_DST_RELEASE for teql interfaces

https://bugzilla.kernel.org/show_bug.cgi?id=16183



The sch_teql module, which can be used to load balance over a set of
underlying interfaces, stopped working after 2.6.30 and has been
broken in all kernels since then for any underlying interface which
requires the addition of link level headers.

The problem is that the transmit routine relies on being able to
access the destination address in the skb in order to do address
resolution once it has decided which underlying interface it is going
to transmit through.

In 2.6.31 the IFF_XMIT_DST_RELEASE flag was introduced, and set by
default for all interfaces, which causes the destination address to be
released before the transmit routine for the interface is called.

The solution is to clear that flag for teql interfaces.

Signed-off-by: Tom Hughes <tom@compton.nu>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>