dscache: Only log unusual memcache errors.

filter/dscache/support.go

Index: filter/dscache/support.go
diff --git a/filter/dscache/support.go b/filter/dscache/support.go
index 4a2480ab7d29162ff37510758d453a2767109e2c..1f8d5cd3e97d57e6604939c97fbc11e8f0d8c6d2 100644
--- a/filter/dscache/support.go
+++ b/filter/dscache/support.go
@@ -117,7 +117,7 @@ func (s *supportContext) mutation(keys []*ds.Key, f func() error) error {
 	}
 	err := f()
 	if err == nil {
-		if err := s.mc.DeleteMulti(lockKeys); err != nil {
+		if err := filterMCErr(s.mc.DeleteMulti(lockKeys)); err != nil {
 			(log.Fields{log.ErrorKey: err}).Warningf(
 				s.c, "dscache: mc.DeleteMulti")
 		}