BUG/MEDIUM: connections: Don't forget to unlock when killing a connection.

Commit 140237471e made sure we hold the
toremove_lock for the corresponding thread before removing a connection
from its idle_orphan_conns list, however it failed to unlock it if we
found a connection, leading to a deadlock, so add the missing deadlock.

This should be backported to 2.1 and 2.0.

src/backend.c

@@ -1255,6 +1255,7 @@ int connect_server(struct stream *s)
 					MT_LIST_ADDQ(&toremove_connections[i],
 					    (struct mt_list *)&tokill_conn->list);
 					task_wakeup(idle_conn_cleanup[i], TASK_WOKEN_OTHER);
+					HA_SPIN_UNLOCK(OTHER_LOCK, &toremove_lock[tid]);
 					break;
 				}
 				HA_SPIN_UNLOCK(OTHER_LOCK, &toremove_lock[tid]);