lnwallet: update MaxHTLCNumber to precisely match the spec
lnwallet: update MaxHTLCNumber to precisely match the spec

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