migration: Use the number of transferred bytes directly

We only use migration_transferred_bytes() to calculate the rate_limit,
for that we don't need to flush whatever is on the qemu_file buffer.
Remember that the buffer is really small (normal case is 32K if we use
iov's can be 64 * TARGET_PAGE_SIZE), so this is not relevant to
calculations.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231025091117.6342-5-quintela@redhat.com>

migration/migration-stats.c

@@ -63,7 +63,7 @@ uint64_t migration_transferred_bytes(QEMUFile *f)
 {
     uint64_t multifd = stat64_get(&mig_stats.multifd_bytes);
     uint64_t rdma = stat64_get(&mig_stats.rdma_bytes);
-    uint64_t qemu_file = qemu_file_transferred(f);
+    uint64_t qemu_file = stat64_get(&mig_stats.qemu_file_transferred);
 
     trace_migration_transferred_bytes(qemu_file, multifd, rdma);
     return qemu_file + multifd + rdma;