The ext4l_ln() function returned -EEXIST when creating a symlink where
a file already exists. This differs from the old ext4 implementation
which deletes any existing file before creating the symlink (like ln -sf
behaviour).
Update ext4l_ln() to match this behaviour by calling __ext4_unlink() to
remove any existing non-directory file before creating the symlink.
Directories cannot be replaced with symlinks and return -EISDIR.
This allows test_symlink3 to pass.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
8eabf8fb91