Update the kernel headers to match external/kernel-headers.

Note that the Linux kernel handed over responsibility for most of the
socket constants to glibc some time ago. Someone had updated our
external/kernel-headers file but not regenerated the bionic headers,
so this change copies the missing stuff from the old bionic <linux/socket.h>
into <sys/socket.h>. This is what glibc does.

I've hacked a few of the other files to #include <sys/socket.h> for
backward compatibility, but even so this requires numerous other
changes to switch people over from direct inclusion of <linux/...> headers.

Change-Id: I0e4af64e631d3cef911a31d90f2f806e058278a0

libc/include/net/if.h

@@ -25,6 +25,8 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
+#include <sys/socket.h>
 #include <linux/if.h>
 #include <sys/cdefs.h>
 #ifndef IF_NAMESIZE