BUG/MINOR: quic: do not consider idle timeout on CLOSING state

BUG/MINOR: quic: do not consider idle timeout on CLOSING state

When entering closing state, a QUIC connection is maintained during a
certain delay. The principle is to ensure the other peer has received
the CONNECTION_CLOSE frame. In case of packet duplication/reordering,
CONNECTION_CLOSE is reemitted.

QUIC RFC recommends to use at least 3 times the PTO value. However,
prior to this patch, haproxy used instead the max value between 3 times
the PTO and the connection idle timeout. In the default case, idle
timeout is set to 30s which is in most of the times largely superior to
the PTO. This has the downside of keeping the connection in memory for
too long whereas all resources could be released much earlier.

Fix this behavior by using 3 times the PTO on closing or draining state.
This value is limited up to 1s. This ensures that most of connections
are covered by this. If a connection runs with a very high RTT, it must
not impact the whole process and should be released in a reasonable
delay.

This should be backported up to 2.6.