[core/swarm] Refactor and extend configurable connection limits. (#1848)

* Refactor and extend configurable connection limits.

To better track different connection counts, permit configurable
limits for these counts and make these available for
inspection efficiently, introduce dedicated connection counters
via a `ConnectionCounters` structure that is exposed on the
API via the `NetworkInfo`. All connection or connection
states that are counted in this way can also have effective
configurable limits.

* Cleanup

* Add missing file.

* Refine naming and config API.

* Update core/CHANGELOG.md

Co-authored-by: Max Inden <mail@max-inden.de>

* Update core/CHANGELOG.md

Co-authored-by: Max Inden <mail@max-inden.de>

Co-authored-by: Max Inden <mail@max-inden.de>

core/src/network/peer.rs

@@ -310,7 +310,7 @@ where
     }
 
     /// The number of established connections to the peer.
-    pub fn num_connections(&self) -> usize {
+    pub fn num_connections(&self) -> u32 {
         self.network.pool.num_peer_established(&self.peer_id)
     }
 
@@ -448,12 +448,6 @@ where
         None
     }
 
-    /// The number of ongoing dialing attempts, i.e. pending outgoing connections
-    /// to this peer.
-    pub fn num_attempts(&self) -> usize {
-        self.network.pool.num_peer_outgoing(&self.peer_id)
-    }
-
     /// Gets an iterator over all dialing (i.e. pending outgoing) connections to the peer.
     pub fn attempts<'b>(&'b mut self)
         -> DialingAttemptIter<'b,
@@ -672,6 +666,15 @@ impl<'a, TInEvent, TOutEvent, THandler, TTransErr, THandlerErr>
 
     /// Obtains the next dialing connection, if any.
     pub fn next<'b>(&'b mut self) -> Option<DialingAttempt<'b, TInEvent>> {
+        // If the number of elements reduced, the current `DialingAttempt` has been
+        // aborted and iteration needs to continue from the previous position to
+        // account for the removed element.
+        let end = self.dialing.get(self.peer_id).map_or(0, |conns| conns.len());
+        if self.end > end {
+            self.end = end;
+            self.pos -= 1;
+        }
+
         if self.pos == self.end {
             return None
         }