Fix remote fallback toggles for ACL and xattr flags

[oferchen]

Summary

• preserve the caller-provided ACL toggle when constructing remote fallback arguments
• treat the xattr toggle identically so future --no-xattrs forwarding works as expected

Testing

• cargo test --package rsync-cli --features acl frontend::tests::remote_fallback_forwards_no_tests::remote_fallback_forwards_no_acls_toggle
• cargo test --package rsync-cli --features acl frontend::tests::remote_fallback_forwards_acls_tests::remote_fallback_forwards_acls_toggle

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https://chatgpt.com/codex/tasks/task_e_690553b8981883238e14f56717329f83