ip: stop propagating argc; optimize ip_parse_common_args

ip: stop propagating argc; optimize ip_parse_common_args

function                                             old     new   delta
find_pair                                            167     187     +20
static.families                                        -      17     +17
die_must_be_on_off                                     -      11     +11
...
on_off                                                33      22     -11
do_ipaddr                                            103      90     -13
do_iptunnel                                         1001     986     -15
iproute_list_or_flush                               1237    1217     -20
static.ip_common_commands                             43      22     -21
do_iproute                                          2217    2193     -24
parse_args                                          1444    1414     -30
ip_do                                                 47      16     -31
do_iprule                                            994     963     -31
ip_main                                              153     113     -40
ipaddr_modify                                       1357    1305     -52
ipaddr_list_or_flush                                2543    2490     -53
ip_parse_common_args                                 294     159    -135
------------------------------------------------------------------------------
(add/remove: 4/1 grow/shrink: 4/24 up/down: 85/-563)         Total: -478 bytes
   text    data     bss     dec     hex filename
 775561     966    9236  785763   bfd63 busybox_old
 775073     962    9236  785271   bfb77 busybox_unstripped