Handling feerates for the fundee (who only receives fee_update) is
simple: it's practically atomic since we accept commitment and send
revocation, thus they're applied to both sides at once.
Handling feerates for the funder is more complex: in theory we could
have multiple in flight. However, if we avoid this using the same
logic as we use to suppress multiple commitments in flight, it's
simple again.
We fix the test code to use real feerate manipulation, thus have to
remove an assert about feerate being non-zero. And now we have
feechanges, we need to rely on the changes_pending flags, as we can
have changes without an HTLCs changing.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Rusty Russell