top: fix memset length (sizeof(ptr) vs sizeof(array) problem)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
sha3: code shrink (and speedup for SHA3_SMALL=0)

function                                             old     new   delta
sha3_process_block72                                1454    1359     -95

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
sha3: tweak comments and indentation

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ftpd: add optional support for authentication

function                                             old     new   delta
cmdio_get_cmd_and_arg                                  -     237    +237
get_passwd                                             -      97     +97
check_password                                         -      82     +82
ftpd_main                                           2297    2178    -119
ask_and_check_password_extended                      206      84    -122
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 0/2 up/down: 416/-241)          Total: 175 bytes

Signed-off-by: Morten Kvistgaard <MK@pch-engineering.dk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>