htlcswitch: ensure links are eligible to forward when selecting outgoing links
htlcswitch: ensure links are eligible to forward when selecting outgoing links

In this commit, when selecting a candidate link to forward a payment,
we’ll ensure that it’s actually able to take on the HTLC. Otherwise,
we’ll skip over the link itself. Currently, a link is only fully
eligible for forwarding, *after* we’ve received and fully processed the
FundingLocked message.

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