Address #1695

Better error messages when the beacon node is asked to listen on a
reserved port (0) or an already taken one.

beacon_chain/eth2_network.nim

@@ -961,8 +961,18 @@ template publicKey*(node: Eth2Node): keys.PublicKey =
 
 proc startListening*(node: Eth2Node) {.async.} =
   if node.discoveryEnabled:
+    try:
        node.discovery.open()
+    except CatchableError as err:
+      fatal "Failed to start discovery service. UDP port may be already in use"
+      quit 1
+
+  try:
     node.libp2pTransportLoops = await node.switch.start()
+  except CatchableError:
+    fatal "Failed to start LibP2P transport. TCP port may be already in use"
+    quit 1
+
   await node.pubsub.start()
 
 proc start*(node: Eth2Node) {.async.} =

vendor/nim-confutils

@@ -1 +1 @@
-Subproject commit 5c81aab54d00bb4cc0921fc9d3ace828b1fcc09f
+Subproject commit 5d8d1ea648884a460518e7819be2d406e3a4ab0f