libifconfig: style(9) and license fixes

[marieheleneka_gmail.com]

Summary

Make code conform to style(9), switch from BSD 3-clause to 2-clause license where possible, and consolidate duplicate 3-clause license into one.

[cem]

LGTM modulo nit below :-).

lib/libifconfig/libifconfig_internal.c

59–61

Some of these lines are probably short enough to be combined.

[marieheleneka_gmail.com]

Fixed minor nit, and fixed up examples as well.

[cem]

LGTM modulo new nit below :-).

lib/libifconfig/libifconfig.c

32–34

This was correct before.

Kernel include files (i.e. sys/*.h) come first; normally, include
<sys/types.h> OR <sys/param.h>, but not both.  <sys/types.h> includes
<sys/cdefs.h>, and it is okay to depend on that.

#include <sys/types.h>  /* Non-local includes in angle brackets. */

For a network program, put the network include files next.

(man 9 style)

[marieheleneka_gmail.com]

Fixed another nit that got broken in previous fix. :)

[marieheleneka_gmail.com]

Fixed missing line, and ordered includes properly in libifconfig_internal.c.

[allanjude]

lib/libifconfig/libifconfig.h

98

danfe@ provided a bunch of style(9) feedback in the previous review: https://reviews.freebsd.org/D7742#160685

You likely want to address that here as well. The return type should be on a separate line from the function name

[cem]

lib/libifconfig/libifconfig.h

98

The return type should be on a separate line from the function name

Not for prototypes, which is what these are. Lots of examples in style(9) of single-line prototypes.

[marieheleneka_gmail.com]

lib/libifconfig/libifconfig.h

98

I see a few examples involving header files in style(9), and prototypes seem to have the type on the same line. Is it safe to assume it's fine?

Prototypes may have an extra space after a tab to enable function names to line up:
     static char     *function(int _arg, const char *_arg2, struct foo *_arg3,
                         struct bar *_arg4);
     static void      usage(void);

[allanjude]

lib/libifconfig/libifconfig.h

98

sorry, my mistake. I was just searching for the function name from the other review, and accidentally hit the prototype. I see that you have already fixed the actual function.

Just wanted to make sure danfe@'s review comments didn't get lost

[cem]

lib/libifconfig/libifconfig.h

98

Yeah, the prototypes are fine as-is. :-)