test: add additional AVB protocol coverage tests (phases 7-8)

Add 26 new tests covering protocol areas not yet exercised:

Phase 7 (12 tests):
- MAAP conflict detection: probe/announce conflicts, defend logic
- ACMP disconnect: RX forwarding, TX without stream, pending timeout
- AECP GET_AVB_INFO: success path and wrong descriptor type
- MRP timers: leave-all and periodic timer verification
- MSRP talker-failed: attribute processing with failure info

Phase 8 (14 tests):
- MVRP: attribute lifecycle, VID packet encoding
- MMRP: attribute type verification (MAC + service requirement)
- ADP: duplicate entity, targeted discover, readvertise, departure
- Descriptor lookup: edge cases, data integrity after add
- AECP commands: GET_CONFIGURATION, GET_SAMPLING_RATE, GET_NAME

Total test count: 72 tests across 8 phases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/test-avb-utils.h

@@ -51,6 +51,7 @@ static inline struct server *avb_test_server_new(struct impl *impl)
 	spa_list_append(&impl->servers, &server->link);
 	spa_hook_list_init(&server->listener_list);
 	spa_list_init(&server->descriptors);
+	spa_list_init(&server->streams);
 
 	if (server->transport->setup(server) < 0)
 		goto error;
@@ -295,6 +296,7 @@ static inline struct server *avb_test_server_new_milan(struct impl *impl)
 	spa_list_append(&impl->servers, &server->link);
 	spa_hook_list_init(&server->listener_list);
 	spa_list_init(&server->descriptors);
+	spa_list_init(&server->streams);
 
 	if (server->transport->setup(server) < 0)
 		goto error;