zcip: another code shrink

zcip: another code shrink

function                                             old     new   delta
send_arp_request                                       -     185    +185
zcip_main                                           1273    1272      -1
pick_nip                                              40       -     -40
arp                                                  185       -    -185
------------------------------------------------------------------------------
(add/remove: 1/2 grow/shrink: 0/1 up/down: 185/-226)          Total: -41 bytes

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