Step 2a (2/2): LLDP transmit, switch shows name and IP

- aes67_net/lldp.c: IEEE 802.1AB LLDPDU sent as a raw frame with
  esp_eth_transmit every 30 s (TTL 120 s) and immediately on a new IP
  or hostname change. TLVs: chassis/port ID (MAC), port description,
  system name (net.hostname), system description (project + version),
  capabilities station-only, IPv4 management address.
- Docs: LLDP in the core Network section; step 2a ticked.
- Verified on an HP 2530-8G-PoE+ (show lldp info remote-device 2): all
  fields shown, management address 192.168.192.244.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/aes67-core-base.md

@@ -92,6 +92,7 @@ When this device is the GM, offset/frequency/delay show "–".
 - Default: one untagged interface. VLAN split option: AES67 untagged + internet tagged (inet.vlan_id/pcp) using the ESP-IDF vlan_support approach (examples/network/vlan_support, ESP32-P4 supported). AES67 side has no gateway; default route and DNS are on inet.
 - PTP, RTP, SAP and IGMP bind to the AES67 netif. HTTP server filters on `web_on`.
 - mDNS (espressif/mdns): `<net.hostname>.local` plus the web UI as `_http._tcp` port 80. A hostname change applies live (the new name answers after ~1 s of RFC 6762 probing).
+- LLDP (IEEE 802.1AB), transmit only, own code (not in IDF/lwIP): every 30 s, TTL 120 s, plus immediately on a new IP or hostname. TLVs: chassis ID and port ID = MAC, port description "eth0", system name = net.hostname, system description = project + firmware version, capabilities station-only, management address = IPv4. With the VLAN split, send it on the AES67 (untagged) side; the 802.1 port VLAN ID TLV can be added then.
 - Switch port: AES67 as native/untagged VLAN, internet tagged, PoE on. IGMP snooping + querier on the AES67 VLAN.
 
 ## Syslog