Add auto_force_rport and auto_comedia NAT options

This patch adds the auto_force_rport and auto_comedia NAT options. It
also converts the nat= setting to a list of comma-separated combinable
options: no, force_rport, comedia, auto_force_rport, and auto_comedia.
nat=yes remains as an undocumented option equal to
"force_rport,comedia". The first instance of 'yes' or 'no' in the list
stops parsing and overrides any previously set options. If an auto_*
option is specified with its non-auto_ counterpart, the auto setting
takes precedence.

This patch builds upon the patch posted to ASTERISK-17860 by JIRA user
pedro-garcia.

(closes issue ASTERISK-17860)
Review: https://reviewboard.asterisk.org/r/1698/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@354597 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sip/include/config_parser.h

@@ -43,6 +43,18 @@ int sip_parse_register_line(struct sip_registry *reg, int default_expiry, const
  */
 int sip_parse_host(char *line, int lineno, char **hostname, int *portnum, enum sip_transport *transport);
 
+/*! \brief Parse the comma-separated nat= option values
+ * \param value The comma-separated value
+ * \param mask An array of ast_flags that will be set by this function
+ *             and used as a mask for copying the flags later
+ * \param flags An array of ast_flags that will be set by this function
+ *
+ * \note The nat-related values in both mask and flags are assumed to empty. This function
+ * will treat the first "yes" or "no" value in a list of values as overiding all other values
+ * and will stop parsing. Auto values will override their non-auto counterparts.
+ */
+void sip_parse_nat_option(const char *value, struct ast_flags *mask, struct ast_flags *flags);
+
 /*!
  * \brief register config parsing tests
  */