xprtrdma: Trace mapping, alloc, and dereg failures

These are rare, but can be helpful at tracking down DMAR and other
problems.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -1392,8 +1392,10 @@ __rpcrdma_dma_map_regbuf(struct rpcrdma_ia *ia, struct rpcrdma_regbuf *rb)
 					    (void *)rb->rg_base,
 					    rdmab_length(rb),
 					    rb->rg_direction);
-	if (ib_dma_mapping_error(device, rdmab_addr(rb)))
+	if (ib_dma_mapping_error(device, rdmab_addr(rb))) {
+		trace_xprtrdma_dma_maperr(rdmab_addr(rb));
 		return false;
+	}
 
 	rb->rg_device = device;
 	rb->rg_iov.lkey = ia->ri_pd->local_dma_lkey;