fix(isn): flip sub-interface naming to real-gear conventions (v0.19.1)

Owner review of the v0.19.0 demo + Cisco docs/real spine CLI verification:
ACI spines name the VLAN-4 sub-if after the PORT (eth1/49.49, cf.
Eth1/29.29-style in show ip ospf neighbors vrf overlay-1); the ISN Nexus
names its dot1q-4 sub-if after the VLAN (Ethernet1/1.4). v0.19.0 had the
two conventions swapped. 908 tests green.

aci_sim/build/fabric.py

@@ -273,12 +273,14 @@ def build(topo: Topology, site: Site, store: MITStore) -> None:
     # ISN CSW LLDP neighbor — multi-site only, one per spine's dedicated ISN
     # uplink PHYSICAL port (eth1/{49+si} — see interfaces.py/underlay.py: the
     # OSPF logical interface on this port is a routed VLAN-4 sub-interface,
-    # "eth1/{49+si}.4", but real LLDP is advertised on the physical port
-    # itself even when a routed sub-if carries the IP, so this adjacency
-    # deliberately targets the base port, not the sub-if). autoACI's Topology
-    # "Fabric (physical)" view derives this uplink row from ospfIf (port +
-    # local IP) + ospfAdjEp (remote IP) + this lldpAdjEp (CSW-side port), so
-    # without it the neighbor port/name show up blank in that view.
+    # "eth1/{49+si}.{49+si}" per the ACI naming convention, but LLDP itself is
+    # advertised per physical port, so this adjacency targets the base port).
+    # The CSW-side port-id follows the IPN/ISN Nexus convention — a dot1q-4
+    # routed sub-interface named after the VLAN ("Ethernet1/x.4", e.g. real
+    # IPN configs `interface Ethernet1/1.4` + `encapsulation dot1q 4`).
+    # autoACI's Topology "Fabric (physical)" view derives this uplink row from
+    # ospfIf (port + local IP) + ospfAdjEp (remote IP) + this lldpAdjEp
+    # (CSW-side port), so without it the neighbor port/name show up blank.
     if len(topo.sites) > 1:
         isn_ip = f"172.16.{site.id}.254"
         for si, spine in enumerate(site.spine_nodes()):
@@ -287,7 +289,7 @@ def build(topo: Topology, site: Site, store: MITStore) -> None:
                 pod=pod,
                 local_node_id=spine.id,
                 local_port=f"eth1/{49 + si}",
-                remote_port=f"Ethernet1/{si + 1}",
+                remote_port=f"Ethernet1/{si + 1}.4",
                 neighbor_name=f"ISN-CSW{site.id}",
                 neighbor_mgmt_ip=isn_ip,
                 neighbor_kind="switch",

aci_sim/build/underlay.py

@@ -95,11 +95,15 @@ def build(topo: Topology, site: Site, store: MITStore) -> None:
             # is now the routed VLAN-4 sub-interface of the eth1/{49+si} ISN
             # uplink port interfaces.py builds a dedicated l1PhysIf for — real
             # ACI multi-site spines carry the ISN-facing OSPF address on this
-            # kind of sub-if, not the bare physical port. `addr` uses the same
-            # /24 as the peer ipn_ip below so the adjacency stays
+            # kind of sub-if, not the bare physical port. NAMING (verified
+            # against real spine CLI, e.g. "Eth1/29.29"/"Eth1/33.33" in
+            # `show ip ospf neighbors vrf overlay-1`): the ACI-side sub-if
+            # NUMBER equals the PORT number — the encap is always vlan-4 but
+            # only the IPN/ISN-router side names its sub-if ".4". `addr` uses
+            # the same /24 as the peer ipn_ip below so the adjacency stays
             # subnet-consistent (consumer: autoACI's fabric_ospf.py, which
             # reads ospfIf.id (falling back to ifId) + area + operSt).
-            if_port = f"eth1/{49 + si}.4"
+            if_port = f"eth1/{49 + si}.{49 + si}"
             if_dn = f"{ospf_base}/if-[{if_port}]"
             store.add(MO(
                 "ospfIf",