lnwallet: properly detect initiator cooperative close in closeObserver
lnwallet: properly detect initiator cooperative close in closeObserver

This commit modifies the logic of the closeObserver slightly to not
incorrectly mark the broadcast of the commitment transaction triggered
by a cooperative channel closure as an unprompted broadcast.

bryanvu/lnd,AndrewSamokhvalov/lnd,ddustin/lnd,aakselrod/lnd,ddustin/lnd,LightningNetwork/lnd,aakselrod/lnd,bryanvu/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd