Mkdir was masking in.Mode with wfs.option.Umask on top of the kernel's
VFS umask pass, so a caller with umask=0 who requested mkdir(0777) got
0755 (0777 & ~022). Create and Symlink don't apply this second pass —
Mkdir was the odd one out. The resulting dirs had fewer write bits than
the caller asked for, which broke cross-user rename permission checks
(kernel may_delete rejects with EACCES when the parent lacks o+w even
though the caller explicitly requested it) and blocked pjdfstest
tests/rename/21.t and its cascading checks.
Drop the extra umask so Mkdir trusts in.Mode exactly like Create. The
CLI -umask flag still covers the internal cache dirs that the mount
creates for itself via os.MkdirAll; only the user-facing Mkdir path
changes.
Unblocks tests/rename/21.t — full pjdfstest suite is now 236 files /
8819 tests, all PASS, and known_failures.txt is empty.