The previous commit (407a0b3) was based on a wrong premise. Userspace
Samba's smbd does NOT implement an SMB-Direct (RDMA) transport even
with --with-smb-direct passed to waf — the flag is silently accepted
but the resulting binary contains no ibverbs code (verified post-
deploy: ldd /bin/smbd shows no libibverbs linkage, smbd doesn't
listen on port 5445, and testparm rejects "smb direct" as an unknown
parameter).

SMB Direct in Linux is implemented in the kernel server `ksmbd`
(net/smb/server/ in the kernel tree), which is a separate
implementation from Samba. ksmbd would lose us:
  - passdb backend = ldapsam (LDAP-backed posix users)
  - Spotlight + tinysparql tracker integration
  - vfs_fruit (metadata stream / macOS attrs / Time Machine sparse-
    bundle support — central to ldx-timemachine share)

Not a worthwhile trade for the SMB workload, which is interactive
Finder browsing not bulk throughput. NFS-over-RDMA on the same
RoCE fabric (mlx4_ib via bond40g) covers the bulk-throughput case
already.

Replaced the misleading "SMB Direct" comment block with an explicit
"why this is NOT enabled" note so this doesn't get re-tried.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>