chacha20 cipher_algbits is 0

[Tim Kuijsten]

Since I'm running postfix with LibreSSL, some clients encrypt the 
connection using ECDHE-RSA-CHACHA20-POLY1305. Now I'm used to seeing 
headers like "using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 
(128/128 bits)" . But these ChaCha20 headers look like "using TLSv1.2 
with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/0 bits)". I'm wondering 
what the 0 part in 256/0 bits mean. I've read it's "the number of bits 
actually used" vs. "the number of bits the algorithm is based on", but 
this sounds confusing to me. Can someone maybe clarify?

Thanks,
Tim