Don't drop Binding Requests in Controlled Agent

A controlled Agent would discard incoming Binding Requests if it didn't
cause the pair to be selected. For UDP Candidate this would be
interpreted as packet loss. For TCP Candidates not responding with a
Binding Success could be interpreted as a failure.

Firefox's ICE Agent would disconnect TCP Candidates because of this
behavior.

Resolves to pion/webrtc#2125
Resolves to pion/webrtc#1356
See https://bugzilla.mozilla.org/show_bug.cgi?id=1756460

selection.go

@@ -240,33 +240,20 @@ func (s *controlledSelector) HandleBindingRequest(m *stun.Message, local, remote
 		p = s.agent.addPair(local, remote)
 	}
 
-	if useCandidate {
+	if useCandidate && p.state == CandidatePairStateSucceeded {
 		// https://tools.ietf.org/html/rfc8445#section-7.3.1.5
 
-		if p.state == CandidatePairStateSucceeded {
-			// If the state of this pair is Succeeded, it means that the check
-			// previously sent by this pair produced a successful response and
-			// generated a valid pair (Section 7.2.5.3.2).  The agent sets the
-			// nominated flag value of the valid pair to true.
-			if selectedPair := s.agent.getSelectedPair(); selectedPair == nil {
-				s.agent.setSelectedPair(p)
-			}
-			s.agent.sendBindingSuccess(m, local, remote)
-		} else {
-			// If the received Binding request triggered a new check to be
-			// enqueued in the triggered-check queue (Section 7.3.1.4), once the
-			// check is sent and if it generates a successful response, and
-			// generates a valid pair, the agent sets the nominated flag of the
-			// pair to true.  If the request fails (Section 7.2.5.2), the agent
-			// MUST remove the candidate pair from the valid list, set the
-			// candidate pair state to Failed, and set the checklist state to
-			// Failed.
-			s.PingCandidate(local, remote)
+		// If the state of this pair is Succeeded, it means that the check
+		// previously sent by this pair produced a successful response and
+		// generated a valid pair (Section 7.2.5.3.2).  The agent sets the
+		// nominated flag value of the valid pair to true.
+		if selectedPair := s.agent.getSelectedPair(); selectedPair == nil {
+			s.agent.setSelectedPair(p)
 		}
-	} else {
-		s.agent.sendBindingSuccess(m, local, remote)
-		s.PingCandidate(local, remote)
 	}
+
+	s.agent.sendBindingSuccess(m, local, remote)
+	s.PingCandidate(local, remote)
 }
 
 type liteSelector struct {