unix: add more illumos Lifreq helpers

This work is in support of wireGuard/wireguard-go#39

Change-Id: Id205d28935b76b49ec6b29aba0a741659c5c01d7
Reviewed-on: https://go-review.googlesource.com/c/sys/+/345610
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Trust: Cherry Mui <cherryyz@google.com>

unix/syscall_illumos.go

@@ -162,6 +162,14 @@ func (l *Lifreq) GetLifruInt() int {
 	return *(*int)(unsafe.Pointer(&l.Lifru[0]))
 }
 
+func (l *Lifreq) SetLifruUint(d uint) {
+	*(*uint)(unsafe.Pointer(&l.Lifru[0])) = d
+}
+
+func (l *Lifreq) GetLifruUint() uint {
+	return *(*uint)(unsafe.Pointer(&l.Lifru[0]))
+}
+
 func IoctlLifreq(fd int, req uint, l *Lifreq) error {
 	return ioctl(fd, req, uintptr(unsafe.Pointer(l)))
 }