udhcp: many small fixes:

udhcp: many small fixes:
* arpping(): smaller and even probably fixed
* lots of variables/params converted: ulong -> uint32_t
* uptime() nuked in favor of monotonic_sec()
* udhcp_get_packet(): only one "bad vendor", simplify

function                                             old     new   delta
reservedIp                                            36      35      -1
udhcpc_main                                         2462    2460      -2
addStaticLease                                        64      62      -2
static.broken_vendors                                 16       -     -16
uptime                                                19       -     -19
udhcpd_main                                         1273    1238     -35
udhcp_get_packet                                     223     184     -39
.rodata                                           144162  144106     -56
arpping                                              690     609     -81
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 0/7 up/down: 0/-251)           Total: -251 bytes
   text    data     bss     dec     hex filename
 734241    3028   14400  751669   b7835 busybox_old
 734005    3028   14400  751433   b7749 busybox_unstripped