fs/smb/client: Use common code in client

Now we've got the common code, use it for the client as well.
Note there's a change here where we're using the server version of
UniStrcat now which had different types (__le16 vs wchar_t) but
it's not interpreting the value other than checking for 0, however
we do need casts to keep sparse happy.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Steve French <stfrench@microsoft.com>