ifenslave: further shrink by suppressing excessive inlining

ifenslave: further shrink by suppressing excessive inlining
ifenslave: reorder functions to avoid forward declarations

function                                             old     new   delta
enslave                                                -     531    +531
get_drv_info                                           -     176    +176
ifenslave_main                                      1411     671    -740
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 0/1 up/down: 707/-740)          Total: -33 bytes
   text    data     bss     dec     hex filename
 809737     624    7060  817421   c790d busybox_old
 809704     624    7060  817388   c78ec busybox_unstripped