dbuf_is_metadata: ensure that it returns B_TRUE or B_FALSE

Without this patch, the

    ASSERT3U(dbuf_is_metadata(db), ==, arc_is_metadata(buf));

at the beginning of dbuf_assign_arcbuf can panic
if the object type is a DMU_OT_NEWTYPE that has
DMU_OT_METADATA set.

Signed-off-by: Christian Schwarz <christian.schwarz@nutanix.com>

module/zfs/dbuf.c

@@ -588,7 +588,7 @@ dbuf_is_metadata(dmu_buf_impl_t *db)
 		boolean_t is_metadata;
 
 		DB_DNODE_ENTER(db);
-		is_metadata = DMU_OT_IS_METADATA(DB_DNODE(db)->dn_type);
+		is_metadata = !!DMU_OT_IS_METADATA(DB_DNODE(db)->dn_type);
 		DB_DNODE_EXIT(db);
 
 		return (is_metadata);

module/zfs/dbuf_stats.c

@@ -87,7 +87,7 @@ __dbuf_stats_hash_table_data(char *buf, size_t size, dmu_buf_impl_t *db)
 	    (longlong_t)db->db_blkid,
 	    (u_longlong_t)db->db.db_offset,
 	    (u_longlong_t)db->db.db_size,
-	    !!dbuf_is_metadata(db),
+	    dbuf_is_metadata(db),
 	    db->db_state,
 	    (ulong_t)zfs_refcount_count(&db->db_holds),
 	    multilist_link_active(&db->db_cache_link),