unix: add SI_LOAD_SHIFT on Linux

This is used to convert the loadavg values read using Sysinfo into
float.

Change-Id: I3866c17c908a463373db89690152acc720c73ef3
Reviewed-on: https://go-review.googlesource.com/c/sys/+/246897
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/linux/types.go

@@ -815,6 +815,8 @@ type FdSet C.fd_set
 
 type Sysinfo_t C.struct_sysinfo
 
+const SI_LOAD_SHIFT = C.SI_LOAD_SHIFT
+
 type Utsname C.struct_utsname
 
 type Ustat_t C.struct_ustat

unix/ztypes_linux.go

@@ -673,6 +673,8 @@ type InotifyEvent struct {
 
 const SizeofInotifyEvent = 0x10
 
+const SI_LOAD_SHIFT = 0x10
+
 type Utsname struct {
 	Sysname    [65]byte
 	Nodename   [65]byte