rxrpc: Trace protocol errors in received packets

Add a tracepoint (rxrpc_rx_proto) to record protocol errors in received
packets.  The following changes are made:

 (1) Add a function, __rxrpc_abort_eproto(), to note a protocol error on a
     call and mark the call aborted.  This is wrapped by
     rxrpc_abort_eproto() that makes the why string usable in trace.

 (2) Add trace_rxrpc_rx_proto() or rxrpc_abort_eproto() to protocol error
     generation points, replacing rxrpc_abort_call() with the latter.

 (3) Only send an abort packet in rxkad_verify_packet*() if we actually
     managed to abort the call.

Note that a trace event is also emitted if a kernel user (e.g. afs) tries
to send data through a call when it's not in the transmission phase, though
it's not technically a receive event.

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

net/rxrpc/sendmsg.c

@@ -623,7 +623,8 @@ int rxrpc_kernel_send_data(struct socket *sock, struct rxrpc_call *call,
 		read_unlock_bh(&call->state_lock);
 		break;
 	default:
-		 /* Request phase complete for this client call */
+		/* Request phase complete for this client call */
+		trace_rxrpc_rx_eproto(call, 0, tracepoint_string("late_send"));
 		ret = -EPROTO;
 		break;
 	}