fixup: don't require exact retransmission if last commit not received…

…: you can just start from prev.

Reported-by: pm47
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

02-peer-protocol.md

@@ -963,9 +963,8 @@ MUST set `revocations_received` to one greater than the commitment number of the
 
 If `commitments_received` is one less than the commitment number of
 the last `commitment_signed` message the receiving node has sent, it
-MUST send a set of `update_` messages against the prior commitment
-transaction followed by `commitment_signed`, otherwise if
-`commitments_received` is not equal to the commitment number of the
+MUST reuse the same commitment number for its next `commitment_signed`,
+otherwise if `commitments_received` is not equal to the commitment number of the
 last `commitment_signed` message the receiving node has sent, it
 SHOULD fail the channel.