New SIP Channel Driver - Add CLI/AMI initiated NOTIFY requests

Added the ability to send unsolicited NOTIFY requests to a particular endpoint
with a configured payload.  Added both CLI and AMI support.  For a given
endpoint, this module will iterate over all its contacts sending the appropriate
NOTIFY request to each.

(closes issue ASTERISK-21436)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2623/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@393364 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/res_sip.h

@@ -1180,6 +1180,13 @@ void ast_copy_pj_str(char *dest, const pj_str_t *src, size_t size);
  */
 struct ast_sip_endpoint *ast_pjsip_rdata_get_endpoint(pjsip_rx_data *rdata);
 
+/*!
+ * \brief Retrieve any endpoints available to sorcery.
+ *
+ * \retval Endpoints available to sorcery, NULL if no endpoints found.
+ */
+struct ao2_container *ast_sip_get_endpoints(void);
+
 /*!
  * \brief Retrieve relevant SIP auth structures from sorcery
  *