IB/addr: Fix IPv6 routing lookup

Include link scope as part of address resolution.  Combine local
and remote address resolution into a single, simpler code path.
Fix error checking in the IPv6 routing lookups.

Based on work from:
David Wilder <dwilder@us.ibm.com>
Jason Gunthorpe <jgunthorpe@obsidianresearch.com>

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
[ Fix up cma_check_linklocal() for !IPV6 case.  - Roland ]

Signed-off-by: Roland Dreier <rolandd@cisco.com>