rxrpc: Fix checker warnings and errors

Fix various issues detected by checker.

Errors:

 (*) rxrpc_discard_prealloc() should be using rcu_assign_pointer to set
     call->socket.

Warnings:

 (*) rxrpc_service_connection_reaper() should be passing NULL rather than 0 to
     trace_rxrpc_conn() as the where argument.

 (*) rxrpc_disconnect_client_call() should get its net pointer via the
     call->conn rather than call->sock to avoid a warning about accessing
     an RCU pointer without protection.

 (*) Proc seq start/stop functions need annotation as they pass locks
     between the functions.

False positives:

 (*) Checker doesn't correctly handle of seq-retry lock context balance in
     rxrpc_find_service_conn_rcu().

 (*) Checker thinks execution may proceed past the BUG() in
     rxrpc_publish_service_conn().

 (*) Variable length array warnings from SKCIPHER_REQUEST_ON_STACK() in
     rxkad.c.

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

net/rxrpc/conn_client.c

@@ -776,7 +776,7 @@ void rxrpc_disconnect_client_call(struct rxrpc_call *call)
 	unsigned int channel = call->cid & RXRPC_CHANNELMASK;
 	struct rxrpc_connection *conn = call->conn;
 	struct rxrpc_channel *chan = &conn->channels[channel];
-	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&call->socket->sk));
+	struct rxrpc_net *rxnet = conn->params.local->rxnet;
 
 	trace_rxrpc_client(conn, channel, rxrpc_client_chan_disconnect);
 	call->conn = NULL;