unix: add missing SizeofIovec constant on Linux

Add the SizeofIovec constant corresponding to type Iovec.

Change-Id: Icde241b8cac3bc89806f0081a4021598bf0ef7cf
Reviewed-on: https://go-review.googlesource.com/51730
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/unix/ztypes_linux_ppc64le.go b/unix/ztypes_linux_ppc64le.go
index 987d481..4deb1e8 100644
--- a/unix/ztypes_linux_ppc64le.go
+++ b/unix/ztypes_linux_ppc64le.go
@@ -379,6 +379,7 @@
 	SizeofSockaddrALG       = 0x58
 	SizeofSockaddrVM        = 0x10
 	SizeofLinger            = 0x8
+	SizeofIovec             = 0x10
 	SizeofIPMreq            = 0x8
 	SizeofIPMreqn           = 0xc
 	SizeofIPv6Mreq          = 0x14