IB/ipoib: Verify address handle validity on send

When the bonding device senses a carrier loss of its active slave it replaces
that slave with a new one. In between the times when the carrier of an IPoIB
device goes down and ipoib_neigh is destroyed, it is possible that the
bonding driver will send a packet on a new slave that uses an old ipoib_neigh.
This patch detects and prevents this from happenning.

Signed-off-by: Moni Shoua <monis at voltaire.com>
Signed-off-by: Or Gerlitz <ogerlitz at voltaire.com>
Acked-by: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>