libbb: introduce and use print_flags().

libbb: introduce and use print_flags().
Mostly by Natanael Copa <natanael.copa AT gmail.com>

function                                             old     new   delta
print_e2flags                                          -     189    +189
print_flags_separated                                  -      86     +86
static.flag_labels                                     -      60     +60
static.dma_wmode_masks                                 -      32     +32
static.flag_masks                                      -      28     +28
static.arp_labels                                      -      16     +16
static.arp_masks                                       -      12     +12
ls_main                                              836     843      +7
...
popstring                                            140     134      -6
arp_show                                             740     708     -32
print_flags                                          189      25    -164
ipaddr_list_or_flush                                2396    2170    -226
process_dev                                         5306    4706    -600
------------------------------------------------------------------------------
(add/remove: 10/0 grow/shrink: 5/10 up/down: 458/-1043)      Total: -585 bytes
   text    data     bss     dec     hex filename
 810564     624    7060  818248   c7c48 busybox_old
 810002     624    7060  817686   c7a16 busybox_unstripped