OK, let's try another approach - include <linux/if.h> rather than

OK, let's try another approach - include <linux/if.h> rather than
<net/if.h>, in the hope that

	1) doing so won't cause some problem somewhere

and

	2) it'll have multiple-include protection

(this whole "glibc is a separate project from the kernel, so we'll
duplicate header files" thing has its downsides).