DF-0207 FIX VALIDATION - clist_alloc_cblocks leak (single-fix kernel #1)

Kernel: DragonFly 6.5-DEVELOPMENT #1: Fri Jul 17 22:18:18 UTC 2026 (DF-0207 fix only)
Harness: df0207_harness.ko, 3000 iterations clist_alloc_cblocks(1024)<->(4096)

=== UNPATCHED #0 baseline (same harness) ===
BEFORE: ttys  Count=37    MemUse=143K    Requests=70
AFTER:  ttys  Count=5.90K MemUse=29.4M   Requests=5.93K   <-- LEAK (29MB orphaned)

=== PATCHED #1 kernel (DF-0207 fix: kfree old c_data) ===
BEFORE: ttys  Count=37    MemUse=143K    Requests=70
AFTER:  ttys  Count=37    MemUse=143K    Requests=5.93K   <-- NO LEAK (old buffers freed)
                                          ^^^^^^^^^^
        MemUse stays FLAT at 143K even though Requests climbed to 5930
        (the kmallocs ran but the old c_data buffers are now kfree()'d).

VERDICT: fix closes the leak. before=29MB leak, after=0 leak.