fix(fwstate): align unicast sync validation with dataplane support

[3Hren]

FWState accepts unicast-only sync configuration, but the dataplane currently recognizes only multicast sync packets.

Affected paths:

• modules/fwstate/controlplane/service.go
• modules/fwstate/dataplane/dataplane.c
• modules/fwstate/controlplane/fwstatepb/fwstate.proto

Problem:

• validateSyncConfig() accepts a config if either multicast or unicast destination address plus port is present.
• is_fw_state_sync_packet() checks multicast Ethernet destination, multicast port, and multicast IPv6 destination only.
• A unicast-only config is accepted by the control plane but will not process matching sync traffic in the dataplane.

Expected outcome:

• Either implement unicast sync packet recognition in the dataplane or reject unicast-only configs until supported.
• Keep validation, proto comments, CLI behavior, and dataplane behavior consistent.
• Add tests for unicast-only and multicast configs.