Change type of oc->last_lru from float back to double

Since the last_lru tracks epoch time, it needs the double precision
floating point type to accurately track the time.

Fixes: #2527

bin/varnishd/cache/cache.h

@@ -376,7 +376,7 @@ struct objcore {
 	uint16_t		oa_present;
 
 	unsigned		timer_idx;	// XXX 4Gobj limit
-	float			last_lru;
+	double			last_lru;
 	VTAILQ_ENTRY(objcore)	hsh_list;
 	VTAILQ_ENTRY(objcore)	lru_list;
 	VTAILQ_ENTRY(objcore)	ban_list;

bin/varnishtest/tests/r02527.vtc

+varnishtest "Test the n_lru_moved counter"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -arg "-p lru_interval=1" -vcl+backend {
+	sub vcl_backend_response {
+		set beresp.do_stream = false;
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+} -run
+
+varnish v1 -expect MAIN.n_lru_moved == 0
+
+delay 1
+
+client c1 {
+	txreq
+	rxresp
+	txreq
+	rxresp
+} -run
+
+varnish v1 -expect MAIN.n_lru_moved == 1