net: Add missing default case in ICMPv4 common function

Author: fwsGonzo

api/net/ip4/icmp4_common.hpp

@@ -95,6 +95,8 @@ namespace net {
           return "TIMESTAMP REPLY (14)";
         case Type::NO_REPLY:
           return "NO REPLY";
+        default:
+          return "UNKNOWN";
       };
     }();
   }