Don't skip a code when going request1->request2 through `Request1
Answer1 Request2`. For example before this patch:

	1		RequestIdentification
	1 | answerBit	AcceptIdentification
	3		Ping
	3 | answerBit	Pong
	...

after this patch:

	1		RequestIdentification
	1 | answerBit	AcceptIdentification
	2		Ping
	2 | answerBit	Pong
	...

This corresponds to NEO/py commit a00ab78b ("protocol: small cleanup in
packet registration").