BUG/MEDIUM: list: correct fix for LIST_POP_LOCKED's removal of last element

As seen with Olivier, in the end the fix in commit 285192564 ("BUG/MEDIUM:
list: fix LIST_POP_LOCKED's removal of the last pointer") is wrong,
the code there was right but the bug was triggered by another bug in
LIST_ADDQ_LOCKED() which doesn't properly update the list's head by
inserting in the wrong order.

This will have to be backported if the commit above is backported.
diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h
index 3b1f599..5cf23df 100644
--- a/include/common/mini-clist.h
+++ b/include/common/mini-clist.h
@@ -216,9 +216,9 @@
 			(el)->n = n;                                       \
 			(el)->p = p;                                       \
 			__ha_barrier_store();                              \
-			n->p = (el);                                       \
+			n->n = (el);                                       \
 			__ha_barrier_store();                              \
-			p->n = (el);                                       \
+			p->p = (el);                                       \
 			__ha_barrier_store();                              \
 			break;                                             \
 		}                                                          \
@@ -299,7 +299,7 @@
 				 __ha_barrier_store();                     \
 				 continue;                                 \
 			 }                                                 \
-			 p2 = HA_ATOMIC_XCHG(&n->p, LLIST_BUSY);           \
+			 p2 = HA_ATOMIC_XCHG(&n2->p, LLIST_BUSY);          \
 			 if (p2 == LLIST_BUSY) {                           \
 				 n->n = n2;                                \
 				 n->p = p;                                 \