icmp: add example and unitest

examples/protocols/icmp_echo/main/cmd_ping.h

@@ -0,0 +1,24 @@
+/* Ping command
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Register Ping command
+ *
+ */
+void register_ping(void);
+
+#ifdef __cplusplus
+}
+#endif
+