move udhcp_{client/server}_config to common_bufsiz1

move udhcp_{client/server}_config to common_bufsiz1

udhcp_run_script                                    1108    1151     +43
init_packet                                          209     210      +1
udhcpc_main                                         2395    2393      -2
udhcp_client_config                                   56       -     -56
udhcp_server_config                                   88       -     -88
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 2/1 up/down: 44/-146)          Total: -102 bytes
   text    data     bss     dec     hex filename
 771326    1029    9696  782051   beee3 busybox_old
 771383    1029    9552  781964   bee8c busybox_unstripped