RDMA/addr: Fix resolution of local IPv6 addresses

This patch allows a local IPv6 address to be resolved by rdma_cm.

To reproduce the problem:

 $ rping -s -v -a ::0  &
 $ rping -c -v -a <IPv6 address local to this system>
 rdma_resolve_addr error -1

Local IPv6 address was obtained with "ip addr show ib0"

Addresses: https://bugs.openfabrics.org/show_bug.cgi?id=1759
Signed-off-by: David Wilder <dwilder@us.ibm.com>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>