Send EZSP v14+ multicasts and broadcasts without a NWK alias

[zigpy-review-bot]

The problem

EZSP v14+ sendMulticast and sendBroadcast were called with alias=0x0000 and sequence= the caller's APS TSN. The stack treats only SL_ZIGBEE_NULL_NODE_ID (0xFFFF) as "not an aliased source": for any other value — including the coordinator's own 0x0000 — it overwrites the NWK source and NWK sequence number of the outgoing frame with the supplied ones.

zigpy's TSNs are not a single counter: Group._send_sequence is per group, and the ZDO/application counters are separate again, all starting at zero. So unrelated frames left the coordinator carrying the same (NWK source, NWK sequence) pair, and routers dropped them as broadcast-transaction-table duplicates for the lifetime of the entry (9 s per the Zigbee PRO stack profile, 20 s on EmberZNet routers). The visible effect is group commands silently doing nothing — see #756 for a full reproduction, and the reporter's confirmation that patching the alias at runtime fixes it on a real network.

The fix

This passes alias=0xFFFF and sequence=0 (ignored without an alias source) for both calls, which lets the stack assign the NWK sequence number itself, as it does on EZSP v13 and older. bellows/zigbee/application.py discards the sequence these two calls return, so nothing depends on the old behaviour.

The stack takes that number from the single per-network NWK counter it also uses for the broadcasts it originates on its own (route requests, link status), so it cannot collide with those — whereas any host-chosen number sent under NWK source 0x0000 can, however it is counted. (From static analysis of the prebuilt EmberZNet 9.0.2 stack library; details in #756.)

Affected versions

Only v14+ is affected: the pre-v14 sendMulticast/sendBroadcast frames have no alias/nwkSequence fields at all (the Gecko SDK exposes aliasing through separate emberSendMulticastWithAlias/emberProxyBroadcast calls instead). The constant value is stable across both SDK generations — EMBER_NULL_NODE_ID is 0xFFFFu in the Gecko SDK and SL_ZIGBEE_NULL_NODE_ID is 0xFFFFu in the Simplicity SDK.

Fixes #756

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.55%. Comparing base (15ccb49) to head (b8f7d39).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #757   +/-   ##
=======================================
  Coverage   99.55%   99.55%           
=======================================
  Files          64       64           
  Lines        4284     4285    +1     
=======================================
+ Hits         4265     4266    +1     
  Misses         19       19           

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