cifs: Do not convert delimiter when parsing NFS-style symlinks

NFS-style symlinks have target location always stored in NFS/UNIX form
where backslash means the real UNIX backslash and not the SMB path
separator.

So do not mangle slash and backslash content of NFS-style symlink during
readlink() syscall as it is already in the correct Linux form.

This fixes interoperability of NFS-style symlinks with backslashes created
by Linux NFS3 client throw Windows NFS server and retrieved by Linux SMB
client throw Windows SMB server, where both Windows servers exports the
same directory.

Fixes: d5ecebc4 ("smb3: Allow query of symlinks stored as reparse points")
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>