unix: add IoctlGetUint32 on Linux

Because the size of int varies on different architectures,
IoctlGetInt is unsuitable for ioctl APIs which explicitly deal with
fixed size integers, such as uint32.

Change-Id: I5a8dc397b713027c4ef9f9a91490f177ac8342e2
Reviewed-on: https://go-review.googlesource.com/c/sys/+/175982
Run-TryBot: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_linux.go

@@ -109,6 +109,12 @@ func IoctlGetInt(fd int, req uint) (int, error) {
 	return value, err
 }
 
+func IoctlGetUint32(fd int, req uint) (uint32, error) {
+	var value uint32
+	err := ioctl(fd, req, uintptr(unsafe.Pointer(&value)))
+	return value, err
+}
+
 func IoctlGetWinsize(fd int, req uint) (*Winsize, error) {
 	var value Winsize
 	err := ioctl(fd, req, uintptr(unsafe.Pointer(&value)))