cd9660: Unbreak symbolic links

Since the introduction of permission masks, cd9660_getattr() returns a
size of zero for all symbolic links, because the code to retrieve the
length of the link target (as required by POSIX) is dead, since we strip
away the type bits before we try to use them to identify the file as a
link. Address this by checking the vnode type instead.

PR: 290556
MFC after: 3 days
Fixes: 82f2275b73e5 ("cd9660: Add support for mask,dirmask,uid,gid options")
Reviewed by: olce
Differential Revision: https://reviews.freebsd.org/D53598