DNS-SD support for multiple KISS ports and AGWPE

Dire Wolf 1.7 introduced the ability to configure multiple KISS TCP
ports, each for a single radio channel. However, DNS Service Discovery
announced only the first configured port. This set of changes expands
DNS-SD support to announce all configured KISS TCP ports, and adds
support for announcing the AGWPE port if configured. The functionality
is available on both Linux and Mac. (Dire Wolf does not currently
support DNS Service Discovery on Windows.)

Details of these changes follow.

On both Linux and Mac:

* All configured KISS TCP and AGWPE ports are announced via DNS-SD.

* Announcement messages include radio channel where appropriate.

* Cleanup code added to gracefully shut down and de-register from
  DNS-SD on exit or error.

* DNS-SD code now checks for services to publish, so that the
  caller doesn't need to do this.

* Standard Dire Wolf style comments added for all functions.

On Linux only:

* Handling of service name collisions is now iterative rather than
  recursive.

* No more gotos.

On Mac only:

* Now-complete implementation includes event loop for handling
  notifications from the DNS-SD daemon, which were previously lost.

* As a consequence of the above, successful announcement message
  now appears in the console (as it did before only for Linux).

* Text color set properly for console messages.

These changes have been tested with as many combinations of config
settings as possible, on Linux Mint 22.1 and macOS Sequoia 15.6.1.

src/direwolf.c

@@ -1137,7 +1137,7 @@ int main (int argc, char *argv[])
 	kissnet_init (&misc_config);
 
 #if (USE_AVAHI_CLIENT|USE_MACOS_DNSSD)
-	if (misc_config.kiss_port[0] > 0 && misc_config.dns_sd_enabled)
+	if (misc_config.dns_sd_enabled)
 	  dns_sd_announce(&misc_config);
 #endif
 
@@ -1692,6 +1692,10 @@ static void cleanup_linux (int x)
 {
 	text_color_set(DW_COLOR_INFO);
 	dw_printf ("\nQRT\n");
+#if (USE_AVAHI_CLIENT|USE_MACOS_DNSSD)
+	if (misc_config.dns_sd_enabled)
+	  dns_sd_term ();
+#endif
 	log_term ();
 	ptt_term ();
 	dwgps_term ();