nilfs2: fix incorrect masking of permission flags for symlinks

The permission flags of newly created symlinks are wrongly dropped on
nilfs2 with the current umask value even though symlinks should have 777
(rwxrwxrwx) permissions:

 $ umask
 0022
 $ touch file && ln -s file symlink; ls -l file symlink
 -rw-r--r--. 1 root root 0 Jun 23 16:29 file
 lrwxr-xr-x. 1 root root 4 Jun 23 16:29 symlink -> file

This fixes the bug by inserting a missing check that excludes
symlinks.

Link: https://lkml.kernel.org/r/1655974441-5612-1-git-send-email-konishi.ryusuke@gmail.com


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: Tommy Pettersson <ptp@lysator.liu.se>
Reported-by: Ciprian Craciun <ciprian.craciun@gmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>