MINOR: quic: Make qc_lstnr_pkt_rcv() be thread safe.

Modify the I/O dgram handler principal function used to parse QUIC packets
be thread safe. Its role is at least to create new incoming connections
add to two trees protected by the same RW lock. The packets are for now on
fully parsed before possibly creating new connections.
diff --git a/src/proto_quic.c b/src/proto_quic.c
index 3b66ff9..2b6bb6a 100644
--- a/src/proto_quic.c
+++ b/src/proto_quic.c
@@ -517,6 +517,7 @@
 	MT_LIST_INIT(&listener->rx.pkts);
 	listener->rx.odcids = EB_ROOT_UNIQUE;
 	listener->rx.cids = EB_ROOT_UNIQUE;
+	HA_RWLOCK_INIT(&listener->rx.cids_lock);
 	default_add_listener(proto, listener);
 }