RDMA/addr: Keep pointer to netdevice in struct rdma_dev_addr

Keep a pointer to the local (src) netdevice in struct rdma_dev_addr,
and copy it in as part of rdma_copy_addr().  Use rdma_translate_ip()
in cma_new_conn_id() to reduce some code duplication and also make
sure the src_dev member gets set.

In a high-availability configuration the netdevice pointer can be used
by the RDMA CM to align RDMA sessions to use the same links as the IP
stack does under fail-over and route change cases.

Signed-off-by: Or Gerlitz <ogerlitz@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>