MXS-1525 Check exact match first when checking host

Given a rule like

  ...
  users %@127.0.0.1 match any rules ...

the code started with %@127.0.0.%, which meant that the exact
match rule would be missed.

server/modules/filter/dbfwfilter/dbfwfilter.cc

@@ -1272,6 +1272,10 @@ static SUser find_user_data(const UserMap& users, std::string name, std::string
         if (it == users.end())
         {
             snprintf(nameaddr, sizeof(nameaddr), "%%@%s", remote.c_str());
+            it = users.find(nameaddr);
+
+            if (it == users.end())
+            {
                 ip_start = strchr(nameaddr, '@') + 1;
 
                 while (it == users.end() && next_ip_class(ip_start))
@@ -1280,6 +1284,7 @@ static SUser find_user_data(const UserMap& users, std::string name, std::string
                 }
             }
         }
+    }
 
     return it != users.end() ? it->second : SUser();
 }