Add memunit to sysinfo(2).

Also properly add padding after Procs in the linux.Sysinfo
structure. This will be implicitly padded to 64bits so we
need to do the same.

PiperOrigin-RevId: 216372907
Change-Id: I6eb6a27800da61d8f7b7b6e87bf0391a48fdb475

pkg/abi/linux/linux.go

@@ -31,6 +31,7 @@ type Sysinfo struct {
 	TotalSwap uint64
 	FreeSwap  uint64
 	Procs     uint16
+	_         [6]byte // Pad Procs to 64bits.
 	TotalHigh uint64
 	FreeHigh  uint64
 	Unit      uint32

pkg/sentry/syscalls/linux/sys_sysinfo.go

@@ -36,6 +36,7 @@ func Sysinfo(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysca
 		Uptime:   t.Kernel().MonotonicClock().Now().Seconds(),
 		TotalRAM: totalSize,
 		FreeRAM:  totalSize - totalUsage,
+		Unit:     1,
 	}
 	_, err := t.CopyOut(addr, si)
 	return 0, nil, err