sunrpc: convert unnecessary GFP_ATOMIC to GFP_NOFS

It's OK to sleep here, we just don't want to recurse into the filesystem
as a writeout could be waiting on this.

Future work: the documentation for GFP_NOFS says "Please try to avoid
using this flag directly and instead use memalloc_nofs_{save,restore} to
mark the whole scope which cannot/shouldn't recurse into the FS layer
with a short explanation why. All allocation requests will inherit
GFP_NOFS implicitly."

But I'm not sure where to do this.  Should the workqueue be arranging
that for us in the case of workqueues created with WQ_MEM_RECLAIM?
Reported-by: Trond Myklebust <trondmy@hammer.space>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/rpcb_clnt.c

@@ -752,7 +752,7 @@ void rpcb_getport_async(struct rpc_task *task)
 		goto bailout_nofree;
 	}
 
-	map = kzalloc(sizeof(struct rpcbind_args), GFP_ATOMIC);
+	map = kzalloc(sizeof(struct rpcbind_args), GFP_NOFS);
 	if (!map) {
 		status = -ENOMEM;
 		dprintk("RPC: %5u %s: no memory available\n",
@@ -770,7 +770,7 @@ void rpcb_getport_async(struct rpc_task *task)
 	case RPCBVERS_4:
 	case RPCBVERS_3:
 		map->r_netid = xprt->address_strings[RPC_DISPLAY_NETID];
-		map->r_addr = rpc_sockaddr2uaddr(sap, GFP_ATOMIC);
+		map->r_addr = rpc_sockaddr2uaddr(sap, GFP_NOFS);
 		if (!map->r_addr) {
 			status = -ENOMEM;
 			dprintk("RPC: %5u %s: no memory available\n",