libibnetdisc: keep cache loadable after port timeouts

[ Upstream commit de83d1c208f9550ec1024a132ad982dcba9d8c06 ]

ibnetdiscover --cache writes each node's port references and each
port's remote-port reference from the in-memory fabric. If a PortInfo
query times out during discovery, the port can remain as a shell in
node->ports[] or as a remoteport without ever being inserted into the
fabric port table. Such a port has no cache port record, but references
to it were still written. ibnd_load_fabric() then rejected the cache with
"Cache invalid: cannot find port".

Make the cache writer emit only references to ports that are actually
serialized. A port is serialized only when it is reachable from its
owning node, and the same predicate is used for node port references,
remote-port references, and port records. References are matched against
a sorted set of serialized ports, avoiding repeated port-table walks on
large fabrics. Keep nodes with no ports array as zero-port node records
so fabric->from_node remains resolvable.

Also tolerate old incomplete caches when reading: missing node port keys
and missing remote ports are skipped instead of aborting the load. While
doing that, keep malformed caches from creating unsafe fabric state by
bounds-checking cached port numbers before indexing node->ports[] (an
out-of-bounds write) and by skipping unclaimed port records before they
are linked into the fabric and then freed (a use-after-free).

Fixes: 01b8045f28f6 ("add libibnetdisc caching to libibnetdiscover")
Signed-off-by: Jonathan Süssemilch Poulain <jpoulain@coreweave.com>
Signed-off-by: Nicolas Morey <nmorey@suse.com>