lnwallet: properly use in KB, not KiB to convert to sat/byte for bitcoind estimator
lnwallet: properly use in KB, not KiB to convert to sat/byte for bitcoind estimator

In this commit, we fix an existing bug. The fee estimation within
bitcoind is based on fee/KB (1000), not fee/KiB (1024).

Pointed out by @dabura667.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd