[4.1] 6831bdd Check against the sampled oc->ban rather than the current oc->ban

[Martin Blix Grydeland]

commit 6831bdd5921cd606d3892cbe8ce7cc37dbfc4e53
Author: Martin Blix Grydeland <martin at varnish-software.com>
Date:   Wed Mar 2 15:05:27 2016 +0100

    Check against the sampled oc->ban rather than the current oc->ban
    
    Without this we could ban an object erranously if the ban lurker has
    moved the OC in the ban list while we were evaluating.

diff --git a/bin/varnishd/cache/cache_ban.c b/bin/varnishd/cache/cache_ban.c
index deb4255..bb06490 100644
--- a/bin/varnishd/cache/cache_ban.c
+++ b/bin/varnishd/cache/cache_ban.c
@@ -556,7 +556,7 @@ BAN_CheckObject(struct worker *wrk, struct objcore *oc, struct req *req)
 
 	oc->ban->refcount--;
 	VTAILQ_REMOVE(&oc->ban->objcore, oc, ban_list);
-	if (b == oc->ban) {
+	if (b == bn) {
 		/* not banned */
 		VTAILQ_INSERT_TAIL(&b0->objcore, oc, ban_list);
 		b0->refcount++;