vmstate: Create optional sections

To make sections optional, we need to do it at the beggining of the code.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/trace-events b/trace-events
index c0111d0..2d395c5 100644
--- a/trace-events
+++ b/trace-events
@@ -1191,6 +1191,7 @@
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
 savevm_section_start(const char *id, unsigned int section_id) "%s, section_id %u"
 savevm_section_end(const char *id, unsigned int section_id, int ret) "%s, section_id %u -> %d"
+savevm_section_skip(const char *id, unsigned int section_id) "%s, section_id %u"
 savevm_state_begin(void) ""
 savevm_state_header(void) ""
 savevm_state_iterate(void) ""