BUG-429: Fix NPE when sending a PCInitiate message

Change-Id: I4c167b5465d200a5293bb6c0b7530b116a0cbf6c
Signed-off-by: Robert Varga <rovarga@cisco.com>
BUG-429: Fix topology not showing prefixes learned from BGP/LS

The Linkstate RIB plugin was losing IP reachability information in the
prefix case. Fix it by using the copy builder constructor.

Also add a defensive check for IP reachability presence in the topology
builder.

Change-Id: I0b16b036397a935771d86a3c7253c998e594ec7c
Signed-off-by: Robert Varga <rovarga@cisco.com>