fix: ack frame

[hax0r31337]

There was a typo for checking against the size of latest_received_pkt_num. As the packet mask is 0b10010000, nFrameType & 0x40 will always be zero.
I changed the mask to 0x10 according to the format documentation.

[hax0r31337]

also got another question, why bother use varint on select lane frame if the max acceptable lane number is 255

[zpostfacto]

Hey, this looks like really great stuff!

I'm swamped right now, but thanks so much for digging into the wire encoding. It looks like you've found a good bug, and are asking good questions. I'll try to get back to you soon.

[hussein-aitlahcen]

@zpostfacto gentle ping on this :)