rxrpc: Trace changes in a call's receive window size

Add a tracepoint (rxrpc_rx_rwind_change) to log changes in a call's receive
window size as imposed by the peer through an ACK packet.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 241e989..45dba73 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -665,6 +665,8 @@ static void rxrpc_input_ackinfo(struct rxrpc_call *call, struct sk_buff *skb,
 			rwind = RXRPC_RXTX_BUFF_SIZE - 1;
 		if (rwind > call->tx_winsize)
 			wake = true;
+		trace_rxrpc_rx_rwind_change(call, sp->hdr.serial,
+					    ntohl(ackinfo->rwind), wake);
 		call->tx_winsize = rwind;
 	}