rds: Lost locking in loop connection freeing

rds: Lost locking in loop connection freeing

upstream commit: 58c490babd4b425310363cbd1f406d7e508f77a5

rds: Lost locking in loop connection freeing

The conn is removed from list in there and this requires
proper lock protection.

Orabug: 19265200

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Guangyu Sun <guangyu.sun@oracle.com>
(cherry picked from commit 92ad60f3efabfcd9eb40e983a131c730829c0d90)