If we're opening a channel with a peer which support anchors (and
we do), we tell fundpsbt/utxopsbt to enforce the emergency reserve;
this matters, as it doesn't know about the channel yet, and thus
won't (if it's our first anchor channel).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: JSON-RPC: `fundchannel` and `multifundchannel` will refuse to spend funds below `min-emergency-msat` if we have any anchor channels (or are opening one).
3e57496af9