Check that a remote funder has enough balance to cover the two anchors

[tankyleo]

This check should include the two anchors that the funder must pay for.

rust-lightning/lightning/src/ln/channel.rs

Line 3511 in d671596

if commitment_stats.remote_balance_msat < commitment_stats.total_fee_sat * 1000 + counterparty_reserve_we_require_msat {

[wpaulino]

It's also missing on the local side when it proposes a fee update.

[tankyleo]

Fixed by #3796