This was only reported for the 'Change Active Layer' operator [which was
not setting the channel as selected in the dopesheet], but this is also
the case elsewhere [where BKE_gpencil_layer_active_set is used], namely:

• gp_layer_remove_exec
• gp_layer_copy_exec
• gp_merge_layer_exec
• gp_layer_change_exec
• gp_layer_active_exec
• gp_stroke_separate_exec

We could set GP_LAYER_SELECT "by hand" in
BKE_gpencil_layer_active_set(), but there is already
animchan_sync_gplayer() that does that. For this, we need the
NA_SELECTED notifier though.