RDMA: Restore ability to fail on AH destroy

Like any other IB verbs objects, AH are refcounted by ib_core. The release
of those objects are controlled by ib_core with promise that AH destroy
can't fail.

Being SW object for now, this change makes dealloc_ah() to behave like any
other destroy IB flows.

Fixes: d345691471 ("RDMA: Handle AH allocations by IB/core")
Link: https://lore.kernel.org/r/20200907120921.476363-3-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/ib_verbs.h

@@ -2403,7 +2403,7 @@ struct ib_device_ops {
 			 struct ib_udata *udata);
 	int (*modify_ah)(struct ib_ah *ah, struct rdma_ah_attr *ah_attr);
 	int (*query_ah)(struct ib_ah *ah, struct rdma_ah_attr *ah_attr);
-	void (*destroy_ah)(struct ib_ah *ah, u32 flags);
+	int (*destroy_ah)(struct ib_ah *ah, u32 flags);
 	int (*create_srq)(struct ib_srq *srq,
 			  struct ib_srq_init_attr *srq_init_attr,
 			  struct ib_udata *udata);
@@ -3596,9 +3596,11 @@ int rdma_destroy_ah_user(struct ib_ah *ah, u32 flags, struct ib_udata *udata);
  *
  * NOTE: for user ah use rdma_destroy_ah_user with valid udata!
  */
-static inline int rdma_destroy_ah(struct ib_ah *ah, u32 flags)
+static inline void rdma_destroy_ah(struct ib_ah *ah, u32 flags)
 {
-	return rdma_destroy_ah_user(ah, flags, NULL);
+	int ret = rdma_destroy_ah_user(ah, flags, NULL);
+
+	WARN_ONCE(ret, "Destroy of kernel AH shouldn't fail");
 }
 
 struct ib_srq *ib_create_srq_user(struct ib_pd *pd,