qcow2: Use dashes instead of underscores in options

This is what QMP wants to use. The options haven't been enabled in any
release yet, so we're still free to change them.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/block/qcow2.h b/block/qcow2.h
index 3b2d5cd..dba9771 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -59,10 +59,10 @@
 #define DEFAULT_CLUSTER_SIZE 65536
 
 
-#define QCOW2_OPT_LAZY_REFCOUNTS "lazy_refcounts"
-#define QCOW2_OPT_DISCARD_REQUEST "pass_discard_request"
-#define QCOW2_OPT_DISCARD_SNAPSHOT "pass_discard_snapshot"
-#define QCOW2_OPT_DISCARD_OTHER "pass_discard_other"
+#define QCOW2_OPT_LAZY_REFCOUNTS "lazy-refcounts"
+#define QCOW2_OPT_DISCARD_REQUEST "pass-discard-request"
+#define QCOW2_OPT_DISCARD_SNAPSHOT "pass-discard-snapshot"
+#define QCOW2_OPT_DISCARD_OTHER "pass-discard-other"
 
 typedef struct QCowHeader {
     uint32_t magic;