svcrpc: make xpo_recvfrom return only >=0

The only errors returned from xpo_recvfrom have been -EAGAIN and
-EAFNOSUPPORT.  The latter was removed by a previous patch.  That leaves
only -EAGAIN, which is treated just like 0 by the caller (svc_recv).

So, just ditch -EAGAIN and return 0 instead.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/svc_xprt.c

@@ -743,7 +743,7 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
 	svc_xprt_received(xprt);
 
 	/* No data, incomplete (TCP) read, or accept() */
-	if (len == 0 || len == -EAGAIN)
+	if (len <= 0)
 		goto out;
 
 	clear_bit(XPT_OLD, &xprt->xpt_flags);

net/sunrpc/svcsock.c

@@ -598,7 +598,7 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 			dprintk("svc: recvfrom returned error %d\n", -err);
 			set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
 		}
-		return -EAGAIN;
+		return 0;
 	}
 	len = svc_addr_len(svc_addr(rqstp));
 	rqstp->rq_addrlen = len;
@@ -1174,13 +1174,13 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 	if (len != -EAGAIN)
 		goto err_other;
 	dprintk("RPC: TCP recvfrom got EAGAIN\n");
-	return -EAGAIN;
+	return 0;
 err_other:
 	printk(KERN_NOTICE "%s: recvfrom returned errno %d\n",
 	       svsk->sk_xprt.xpt_server->sv_name, -len);
 	set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
 err_noclose:
-	return -EAGAIN;	/* record not complete */
+	return 0;	/* record not complete */
 }
 
 /*