Install a dummy SIGHUP handler for non p2p mode

When sending SIGHUP handler, p2p will reload the configuration, while
non-p2p will exit.  Instead of that we install a dummy handler, which
logs that topology reloading for non-p2p is not supported, which
prevents haskell runtime to use the default signal handler (which forces
the process to exit).

Fixes #3872.

cardano-node/src/Cardano/Node/Run.hs

@@ -423,6 +423,15 @@ handleSimpleNode runP p2pMode tracers nc onKernel = do
               , srnMaybeMempoolCapacityOverride = ncMaybeMempoolCapacityOverride nc
               }
       DisabledP2PMode -> do
+#ifdef UNIX
+        _ <- Signals.installHandler
+              Signals.sigHUP
+              (Signals.Catch $ do
+                traceWith (startupTracer tracers)
+                        $ NetworkConfigUpdateError "not supported in non-p2p mode"
+              )
+              Nothing
+#endif
         eitherTopology <- TopologyNonP2P.readTopologyFile nc
         nt <- either (\err -> panic $ "Cardano.Node.Run.handleSimpleNodeNonP2P.readTopologyFile: " <> err) pure eitherTopology
         let (ipProducerAddrs, dnsProducerAddrs) = producerAddressesNonP2P nt