chan_pjsip: Add 'pjsip show channelstats'

Added the ability to show channel statistics to chan_pjsip (cli_functions.c)

Moved the existing 'pjsip show channel(s)' functionality from
pjsip_configuration to cli_functions.c.  The stats needed chan_pjsip's
private header so it made sense to move the existing channel commands as well.

Now using stasis_cache_dump to get the channel snapshots rather than retrieving
all endpoints, then getting each one's channel snapshots.  Much more efficient.

Change-Id: I03b114522126d27434030b285bf6d531ddd79869

channels/pjsip/include/cli_functions.h

@@ -0,0 +1,45 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2016, Fairview 5 Engineering, LLC.
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*!
+ * \file
+ *
+ * \author \verbatim George Joseph <george.joseph@fairview5.com> \endverbatim
+ *
+ * \brief PJSIP CLI functions header file
+ */
+
+#ifndef _PJSIP_CLI_FUNCTIONS
+#define _PJSIP_CLI_FUNCTIONS
+
+
+/*!
+ * \brief Registers the channel cli commands
+ * \since 13.9.0
+ *
+ * \retval 0 on success
+ * \retval -1 on failure
+ */
+int pjsip_channel_cli_register(void);
+
+/*!
+ * \brief Unregisters the channel cli commands
+ * \since 13.9.0
+ */
+void pjsip_channel_cli_unregister(void);
+
+
+#endif /* _PJSIP_CLI_FUNCTIONS */