httpd: explain IP/mask parsing, and simplify it a bit.

parse_conf                                          1258    1247     -11
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(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-11)             Total: -11 bytes
   text    data     bss     dec     hex filename
 772602    1058   11092  784752   bf970 busybox_old
 772594    1058   11092  784744   bf968 busybox_unstripped

1 file changed