ETCM-168: Add kademlia-alpha to config.

src/main/resources/application.conf

@@ -93,6 +93,9 @@ mantis {
       # Timeout to collect all possible responses for a FindNode request.
       kademlia-timeout = 7.seconds
 
+      # Level of concurrency during lookups and enrollment.
+      kademlia-alpha = 3
+
       # Maximum number of messages in the queue associated with a UDP channel.
       channel-capacity = 100
     }

src/main/scala/io/iohk/ethereum/network/discovery/DiscoveryConfig.scala

@@ -16,6 +16,7 @@ case class DiscoveryConfig(
     requestTimeout: FiniteDuration,
     kademliaTimeout: FiniteDuration,
     kademliaBucketSize: Int,
+    kademliaAlpha: Int,
     channelCapacity: Int
 )
 
@@ -36,6 +37,7 @@ object DiscoveryConfig {
       requestTimeout = discoveryConfig.getDuration("request-timeout").toMillis.millis,
       kademliaTimeout = discoveryConfig.getDuration("kademlia-timeout").toMillis.millis,
       kademliaBucketSize = discoveryConfig.getInt("kademlia-bucket-size"),
+      kademliaAlpha = discoveryConfig.getInt("kademlia-alpha"),
       channelCapacity = discoveryConfig.getInt("channel-capacity")
     )
   }

src/main/scala/io/iohk/ethereum/network/discovery/PeerDiscoveryManager.scala

@@ -184,6 +184,7 @@ object PeerDiscoveryManager extends LazyLogger {
       requestTimeout = discoveryConfig.requestTimeout,
       kademliaTimeout = discoveryConfig.kademliaTimeout,
       kademliaBucketSize = discoveryConfig.kademliaBucketSize,
+      kademliaAlpha = discoveryConfig.kademliaAlpha,
       // Discovery is going to enroll with all the bootstrap nodes.
       // In theory we could pass the known nodes as well which Mantis
       // persisted, but that could be a lot more, leading to prolonged