unix: add socket error queue constants and types from linux/errqueue.h

Also add additional packet timestamping constants and types defined
in the same header.

Change-Id: I4280f925b46e229f4c3a83a7fee4612592314016
Reviewed-on: https://go-review.googlesource.com/c/158761
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/mkerrors.sh

@@ -182,6 +182,7 @@ struct ltchars {
 #include <sys/signalfd.h>
 #include <sys/socket.h>
 #include <sys/xattr.h>
+#include <linux/errqueue.h>
 #include <linux/if.h>
 #include <linux/if_alg.h>
 #include <linux/if_arp.h>