lnd: require channel_type negotiation for all channels, and make anchor channels default

[Roasbeef]

We should make anchor channels the default, given most of the implementations have implemented it, and are ready to do the same. Along the way, we should require channel_type based negotiation the default, as without it, channel type negotiation may be unknown/undefined.

Along the way, we should update the itests and the protocol cfg flags to make anchor channels the default. This may require a slight re-work of some of the tests.

Steps To Completion

• Make the channel type, and anchor channel bits required.

• Reject incoming channel requests if they don't use channel type based negotiation.

• Reject incoming channel requests for normal static key channels (non-anchor).