rxrpc: Add tracepoint for ACK proposal

Add a tracepoint to log proposed ACKs, including whether the proposal is
used to update a pending ACK or is discarded in favour of an easlier,
higher priority ACK.

Whilst we're at it, get rid of the rxrpc_acks() function and access the
name array directly.  We do, however, need to validate the ACK reason
number given to trace_rxrpc_rx_ack() to make sure we don't overrun the
array.

Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/output.c

@@ -210,7 +210,8 @@ int rxrpc_send_call_packet(struct rxrpc_call *call, u8 type)
 			rxrpc_propose_ACK(call, pkt->ack.reason,
 					  ntohs(pkt->ack.maxSkew),
 					  ntohl(pkt->ack.serial),
-					  true, true);
+					  true, true,
+					  rxrpc_propose_ack_retry_tx);
 			break;
 		case RXRPC_PACKET_TYPE_ABORT:
 			break;