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/recvmsg.c

@@ -682,9 +682,11 @@ out:
 	return ret;
 
 short_data:
+	trace_rxrpc_rx_eproto(call, 0, tracepoint_string("short_data"));
 	ret = -EBADMSG;
 	goto out;
 excess_data:
+	trace_rxrpc_rx_eproto(call, 0, tracepoint_string("excess_data"));
 	ret = -EMSGSIZE;
 	goto out;
 call_complete: