runtime: fix netbsd build

TBR=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/140220043

src/pkg/runtime/defs_netbsd_386.h

@@ -149,7 +149,7 @@ struct KeventT {
 	uint32	flags;
 	uint32	fflags;
 	int64	data;
-	int32	udata;
+	byte	*udata;
 };
 
 

src/pkg/runtime/defs_netbsd_amd64.h

@@ -154,7 +154,7 @@ struct KeventT {
 	uint32	fflags;
 	byte	Pad_cgo_0[4];
 	int64	data;
-	int64	udata;
+	byte	*udata;
 };
 
 

src/pkg/runtime/defs_netbsd_arm.h

@@ -153,7 +153,7 @@ struct KeventT {
 	uint32	flags;
 	uint32	fflags;
 	int64	data;
-	int32	udata;
+	byte	*udata;
 };