cifs: Increase size of tmp_buf in cifs_readdir to avoid potential overflows

cifs: Increase size of tmp_buf in cifs_readdir to avoid potential overflows

Commit 7b0c8fcff47a885743125dd843db64af41af5a61 refreshed and use
a #define from commit f58841666bc22e827ca0dcef7b71c7bc2758ce82.

cifs: Increase size of tmp_buf in cifs_readdir to avoid potential overflows

Increase size of tmp_buf to possible maximum to avoid potential
overflows. Also moved UNICODE_NAME_MAX definition so that it can be used
elsewhere.

Pointed-out-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>