CVE-2023-34968: mdssvc: cache and reuse stat info in struct sl_inode_path_map
Prepare for the "path" being a fake path and not the real server-side
path where we won't be able to vfs_stat_fsp() this fake path. Luckily we already
got stat info for the object in mds_add_result() so we can just pass stat info
from there.