dbd: clear AFPVOL_NOV2TOEACONV flag to allow AD to xattr conversion

[rdmark]

when afp.conf is set to 'convert appledouble = no' we enable the AFPVOL_NOV2TOEACONV flag, however the dbd tool should always be allowed to convert AD to xattr so clear the flag when running dbd

[augmentcode]

🤖 Augment PR Summary

Summary: dbd now clears AFPVOL_NOV2TOEACONV when v2→EA conversion (DBD_FLAGS_V2TOEA) is requested.
Why: This allows AppleDouble-to-xattr migration to run even if afp.conf has convert appledouble = no.

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[augmentcode]

Review completed. No suggestions at this time.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

📊 Performance Dashboard

Commit: e0b39f76200a8bd0d8ea6989fd611b81cf47b7fe

🔥 Spectest (AFP 3.4) - FlameGraph

Netatalk Code-time: 2.0% · Runtime: 68s · Stacks: 1148

🔥 Click the preview to open the interactive flamegraph (zoom + search).

🔝 Top 10 leaf functions

Function	Samples
_raw_spin_unlock_irqrestore	297684450
do_syscall_64	148842225
find_get_block_common	63947030
__cp_end	61741960
srso_alias_safe_ret	55126750
x64_sys_call	44101400
afpd	39691260
xas_load	36383655
memcmp	36383655
ext4_xattr_cmp	31973515

📈 Speedtest (AFP 3.4) - PerfGraph

🔝 Peak throughput per operation

Operation	Peak mean (MB/s)
Read	6430
Write	1436
Copy	2354
ServerCopy	3288

⏱️ Lantest (AFP 3.4) - LatencyGraph

Avg total runtime: 5068 ms · Avg time per AFP op: 0.098 ms

🐢 All operations (avg runtime, in test order)

Test	Avg (ms)
Writing one large file	40
Reading one large file	15
Creating 2000 files	808
Writing 1024 bytes to 2000 files	429
Lock then unlock 2000 open forks	178
Stat, open, read 512 bytes, close 2000 files	937
Enumerate dir with 2000 files	6
Deleting 2000 files	736
Byte-range lock/unlock 2000 ranges in one fork	178
Create directory tree with 1000 dirs	429
Directory cache hits (20 dirs x 100 files)	109
Mixed cache operations (create/stat/enum/delete) on 1000 files	768
Deep path traversal (20 levels x 100 walks)	119
Cache validation (2000 files x 3 lookups)	316

[andylemin]

@rdmark this had quite a performance hit having it always check, so forcing on always for dbd is may be a performance regression.

I think we need to restrict this to just the dbd tooling rather than the whole dbd backend?

[rdmark]

@andylemin this has nothing to do with the CNID backend of the same name: the code modified here is only ever executed by the dbd command