CLEANUP: quic: use static qualifer on quic_close

quic_close can be used through xprt-ops and can thus be kept as a static
symbol.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index a86e7f7..a1fb283 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -3859,7 +3859,7 @@
 	TRACE_PROTO("QUIC conn. freed", QUIC_EV_CONN_FREED, qc);
 }
 
-void quic_close(struct connection *conn, void *xprt_ctx)
+static void quic_close(struct connection *conn, void *xprt_ctx)
 {
 	struct ssl_sock_ctx *conn_ctx = xprt_ctx;
 	struct quic_conn *qc = conn_ctx->qc;