BUG/MINOR: checks: Rely on next I/O oriented rule when waiting for a connection

BUG/MINOR: checks: Rely on next I/O oriented rule when waiting for a connection

In tcpcheck_main(), when we are waiting for a connection, we must rely on the
next connect/send/expect rule to subscribe to I/O events, not on the immediate
next rule. Because, if it is a set-var or an unset-var rule, we will not
subscribe to I/O events while it is in fact mandatory because a send or an
expect rule is coming. It is required to wake-up the health check as soon as I/O
are possible, instead of hitting a timeout.

No backport needed.

(cherry picked from commit 758d48f54cc3372c2d8e7c34b926d218089c533a)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>