windows: use uint32 for serial comm flags for consistency

This is a follow-up to https://go-review.googlesource.com/c/sys/+/572295
and specifically the comment
https://go-review.googlesource.com/c/sys/+/572295/comment/a00e1a2e_e3b01666/.

All other structs and methods us uint32 in golang.org/x/sys/windows
for flag bitmasks, so make the serial communication structs use uint32
to be consistent with the rest of the package.

As a side effect the DTR_CONTROL_* and RTS_CONTROL_* constants are
updated to reflect the positions of the bits in the 32-bit flags.

Change-Id: Ie19774a8ef5411d7df1e5b0d36806aa1d401fa86
GitHub-Last-Rev: bc93d94
GitHub-Pull-Request: #189
Reviewed-on: https://go-review.googlesource.com/c/sys/+/575635
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>

Author: twpayne

windows/syscall_windows.go

@@ -1864,14 +1864,14 @@ const (
 	CBR_128000 = 128000
 	CBR_256000 = 256000
 
-	DTR_CONTROL_DISABLE   = 0x00
-	DTR_CONTROL_ENABLE    = 0x01
-	DTR_CONTROL_HANDSHAKE = 0x02
-
-	RTS_CONTROL_DISABLE   = 0x00
-	RTS_CONTROL_ENABLE    = 0x01
-	RTS_CONTROL_HANDSHAKE = 0x02
-	RTS_CONTROL_TOGGLE    = 0x03
+	DTR_CONTROL_DISABLE   = 0x00000000
+	DTR_CONTROL_ENABLE    = 0x00000010
+	DTR_CONTROL_HANDSHAKE = 0x00000020
+
+	RTS_CONTROL_DISABLE   = 0x00000000
+	RTS_CONTROL_ENABLE    = 0x00001000
+	RTS_CONTROL_HANDSHAKE = 0x00002000
+	RTS_CONTROL_TOGGLE    = 0x00003000
 
 	NOPARITY    = 0
 	ODDPARITY   = 1

windows/types_windows.go

@@ -3382,15 +3382,15 @@ type BLOB struct {
 }
 
 type ComStat struct {
-	Flags    [4]uint8
+	Flags    uint32
 	CBInQue  uint32
 	CBOutQue uint32
 }
 
 type DCB struct {
 	DCBlength  uint32
 	BaudRate   uint32
-	Flags      [4]uint8
+	Flags      uint32
 	wReserved  uint16
 	XonLim     uint16
 	XoffLim    uint16