- etcp_connections.h: add WIRE_OVERHEAD, IP_UDP_OVERHEAD_V4/V6, SC_ENCRYPT_OVERHEAD
(properly accounts for v6 IP(40)+UDP(8)+SC(3)+CCM tag(16) = 67 vs old UDP_HDR_SIZE=28)
- etcp_connections.c etcp_encrypt_send: use WIRE_OVERHEAD instead of UDP_HDR_SIZE
- etcp_connections.c send_init_response: clamp padding to max_data = mtu - WIRE_OVERHEAD
- chat_core_priv.h: add addr_type_from_ip() classifier
- chat_profile.c, chat_sync.c, member_sync.c: use classified addr_type instead of hardcoded 0
- chat_sync.c: skip zero nat_addr in JOIN, fall back to interface_addr
- topo_node_sqlite.c, member_sync.c: remove addr_type=0 filter from SELECT/DELETE
- chat_profile.c, member_sync.c: DELETE all addresses (not just addr_type=0)