The main change here is that the previously-optional open/accept
fields and reestablish fields are now compulsory (everyone was
including them anyway). In fact, the open/accept is a TLV
because it was actually the same format.
For more details, see lightning-rfc/f068dd0d8dfa5ae75feedd99f269e23be4777381
Changelog-Removed: protocol: support for optioned form of reestablish messages now compulsory.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>