IB/addr: Simplify resolving IPv4 addresses

Merge resolve local/remote address resolution into a single
data flow to ensure consistent access and use of the local routing
tables.

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

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>