channeld: allow remote node to exceed their own HTLC count limits.

[rustyrussell]

We try not to exceed either side, but the spec still allows them to
(we don't, but older nodes would have, as could other implementations).

Fixes: #3953
Changelog-Fixed: protocol: overzealous close when peer sent more HTLCs than they'd told us we could send.
Signed-off-by: Rusty Russell [email protected]

[cdecker]

Code seems fine, just for clarification: this is preventing us from adding a new HTLC to an outgoing channel, caused by a forwarded payment, this is not meant to protect against the peer with whom we share the channel from adding more HTLCs than we'd like to have to the channel (which we might be funder of and thus paying fees for), correct?

ACK 260032b

[rustyrussell]

Code seems fine, just for clarification: this is preventing us from adding a new HTLC to an outgoing channel, caused by a forwarded payment, this is not meant to protect against the peer with whom we share the channel from adding more HTLCs than we'd like to have to the channel (which we might be funder of and thus paying fees for), correct?

ACK 260032b

No, they could never add more than we allowed. But they could add more than they allowed! That's how the spec was written. This behavior change should have been codified in the spec (that you take the min of the two values), but until it is and everyone is upgraded, we'll break channels if it happens.