KeepAlive impl does not respect spec

[mostroverkhov]

• Client assumes KeepAlives are optional, and this not true according to spec: for SETUP frame, Time Between KEEPALIVE Frames must be > 0.

• In above case client still sends ackTimeout as Time Between KEEPALIVE Frames in SETUP (which is not 0 by default), but never actual KA frames, which for properly implemented server leads to connection close due to missing KA.

• Client sends ackTimeout instead of tickInterval as Time Between KEEPALIVE Frames, and missedAcks*ackTimeout for Max Lifetime. But for its own KA bookkeeping client uses formula (roughly) ackTimeout + missedAcks*tickInterval, which leads to significantly delayed connection close by properly implemented server.

• Server does not have received KA frames bookkeeping at all, which possibly leads to indefinite hang

[mostroverkhov]

closed by #529