fail2ban: Reset the counter upon successful login

This is for SASL: when multiple mechanisms available it's kinda expected
that some of them can fail, e.g. if client attempted EXTERNAL without
providing the cert first.

modules/fail2ban.cpp

@@ -216,6 +216,10 @@ class CFailToBanMod : public CModule {
             Add(sRemoteIP, 1);
     }
 
+    void OnClientLogin() override {
+        Remove(GetClient()->GetRemoteIP());
+    }
+
     EModRet OnLoginAttempt(std::shared_ptr<CAuthBase> Auth) override {
         // e.g. webadmin ends up here
         const CString& sRemoteIP = Auth->GetRemoteIP();