BUG/MINOR: tcpcheck: Disable QUICKACK only if data should be sent after connect

BUG/MINOR: tcpcheck: Disable QUICKACK only if data should be sent after connect

It is only a real problem for agent-checks when there is no agent string to
send. The condition to disable TCP_QUICKACK was only based on the action
type following the connect one. But it is not always accurate. indeed, for
agent-checks, there is always a SEND action. But if there is no "agent-send"
string defined, nothing is sent. In this case, this adds 200ms of latency
with no reason.

To fix the bug, a flag is now used on the CONNECT action to instruct there
are data that should be sent after the connect. For health-checks, this flag
is set if the action following the connect is a SEND action. For
agent-checks, it is set if an "agent-send" string is defined.

This patch should fix the issue #1836. It must be backported as far as 2.2.