arping: fix a bug where there is implicit count of 4G;

arping: fix a bug where there is implicit count of 4G;
eliminate data/bss usage; code shrink

function                                             old     new   delta
timeout_us                                             4       -      -4
static.start                                           4       -      -4
src                                                    4       -      -4
sock                                                   4       -      -4
sent                                                   4       -      -4
req_recv                                               4       -      -4
received                                               4       -      -4
last                                                   4       -      -4
dst                                                    4       -      -4
count                                                  4       -      -4
brd_sent                                               4       -      -4
brd_recv                                               4       -      -4
catcher                                              375     365     -10
me                                                    20       -     -20
he                                                    20       -     -20
arping_main                                         1941    1874     -67
------------------------------------------------------------------------------
(add/remove: 0/14 grow/shrink: 0/2 up/down: 0/-165)          Total: -165 bytes
   text    data     bss     dec     hex filename
 783035     941    9244  793220   c1a84 busybox_old
 782907     937    9156  793000   c19a8 busybox_unstripped