[Toybox] [CLEANUP] ifconfig commit 864

[Rob Landley]

Commit http://landley.net/hg/toybox/rev/864

Move the next pointer of struct _iface_list to the start of the struct 
so we can use the llist infrastructure. Collate iface_flags_str[] to 
take up fewer lines.

Remove set_data() from the prototype list because we're going to inline 
it everywhere it's used.

Add an xioctl() wrapper to error_exit() for us if the ioctl fails. (This 
may move to lib/ later on, but doesn't need to yet. The error message 
isn't quite as descriptive, but "SIOCGIFNAME" wasn't hugely user 
friendly either.) At the same time remove set_data() and inline it 
everywhere it's used, it's mostly just xioctl().

More whitespace changes and error_exit() help string trimming. Don't 
combine perror_exit() with gai_strerror(), use error_exit() instead so 
we don't add an extra (confusing) strerror(errno) after the 
gai_strerror() text.

While inlining set_data() and adjusting curly brackets, remove a "// end 
of thingy" comment where the corresponding "if (thingy)" is only three 
lines earlier. It's not needing and nothing else around here is doing it 
so that makes it inconsistent as well.

Remove more NOP return; statements at the end of void functions.