pvmove: add missing segment merging

When pvmove is finished and metadata are updated, the code missed
to merge possible mergable segments - so add explicit merging
call after pvmoved volumes are unlocked.

This avoids weird results where i.e. lvs could have been reporting
non-matching segments as lvs upon metadata read is doing silent segment
merging while dm table left after pvmove was still preserving
non-merged segments.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.177 -
 ====================================
+  Merge segments when pvmove is finished.
   Remove label_verify that has never been used.
   Ensure very large numbers used as arguments are not casted to lower values. 
   Enhance reading and validation of options stripes and stripes_size.

lib/metadata/lv_manip.c

@@ -6637,6 +6637,8 @@ int remove_layers_for_segments_all(struct cmd_context *cmd,
 	dm_list_iterate_items(lvl, lvs_changed) {
 		/* FIXME Assumes only one pvmove at a time! */
 		lvl->lv->status &= ~LOCKED;
+		if (!lv_merge_segments(lvl->lv))
+			return_0;
 	}
 
 	return 1;