udhcp: code shrink; disable time and log server options

udhcp: code shrink; disable time and log server options

function                                             old     new   delta
add_server_options                                     -     100    +100
udhcp_add_simple_option                               92      90      -2
nobody_responds_to_arp                                88      85      -3
dhcp_options                                          66      62      -4
udhcp_add_option_string                              104      94     -10
udhcp_run_script                                     665     654     -11
dhcp_option_strings                                  203     188     -15
static.blank_chaddr                                   16       -     -16
send_ACK                                             211     180     -31
add_bootp_options                                     61       -     -61
udhcpd_main                                         1925    1846     -79
------------------------------------------------------------------------------
(add/remove: 1/2 grow/shrink: 0/8 up/down: 100/-232)         Total: -132 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>