lnwallet: add funding tx p2sh output to lnchannel
lnwallet: add funding tx p2sh output to lnchannel

* Allows for quick access to the pkScript when signing new commitment
transactions.

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