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>
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 99e4c0a..8c7f3de 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -141,7 +141,8 @@
 	ASSERTCMP(call->rx_hard_ack, ==, call->rx_top);
 
 	if (call->state == RXRPC_CALL_CLIENT_RECV_REPLY) {
-		rxrpc_propose_ACK(call, RXRPC_ACK_IDLE, 0, 0, true, false);
+		rxrpc_propose_ACK(call, RXRPC_ACK_IDLE, 0, 0, true, false,
+				  rxrpc_propose_ack_terminal_ack);
 		rxrpc_send_call_packet(call, RXRPC_PACKET_TYPE_ACK);
 	}