ifenslave: fix improper longopts definition

ifenslave: fix improper longopts definition
ifenslave: shrink

function                                             old     new   delta
set_hwaddr                                             -      45     +45
set_ifrname_and_do_ioctl                               -      26     +26
set_mtu                                                -      25     +25
ioctl_on_skfd                                          -      13     +13
static.ifenslave_longopts                             31      34      +3
set_if_up                                             39      36      -3
set_if_down                                           39      36      -3
set_if_flags                                          38      26     -12
static.ifra                                           32      16     -16
get_slave_flags                                       40      24     -16
get_if_settings                                       98      67     -31
set_slave_mtu                                         37       -     -37
set_slave_hwaddr                                      52       -     -52
set_master_hwaddr                                     52       -     -52
ifenslave_main                                      1566    1411    -155
------------------------------------------------------------------------------
(add/remove: 4/3 grow/shrink: 1/7 up/down: 112/-377)         Total: -265 bytes
   text    data     bss     dec     hex filename
 810002     624    7060  817686   c7a16 busybox_old
 809737     624    7060  817421   c790d busybox_unstripped