[thineshvs-google]

Part 4 of 9 for upstreaming L2 VLAN, bridge learning, and FDB support (splitting #722 into self-contained PRs under 150 LOC each; tracked in b/575886032).

Summary of Changes

• dataplane/saiserver/fdb.go:
  • Add subscriber management (subscribe, sendNotification) on fdb to broadcast FdbEventNotificationResponse events (FDB_EVENT_LEARNED, FDB_EVENT_AGED) to active notification channels.
  • Implement CreateFdbEntry and CreateFdbEntries to resolve the target BridgePortId OID to its physical PortId via attrmgr, program the unicast MAC forwarding entry (PACKET_FIELD_NUM_ETHER_MAC_DST -> TransmitAction(portID)) into the "fdb" table, and emit FDB_EVENT_LEARNED.
  • Implement RemoveFdbEntry and RemoveFdbEntries to remove the MAC entry from both the internal fwdbridge.Table learned-MAC cache (brTable.Remove(mac)) and the dataplane "fdb" table, and emit FDB_EVENT_AGED.
• dataplane/saiserver/bridge_test.go:
  • Add TestCreateAndRemoveFdbEntry verifying FDB entry creation, removal, and LEARNED / AGED notification delivery.
• dataplane/saiserver/BUILD:
  • Add //dataplane/forwarding/fwdtable/bridge dependency to saiserver.

Testing

• bazel test //dataplane/saiserver/...