res_pjsip_endpoint_identifier_ip: Unregister the module for headers.

Asterisk uses Reference Counting to track whether a module can be unloaded.
Every consumer who requires a module, increases the reference count. When the
consumer goes, is unloaded itself, it has to decrease the reference count on
all its used/required modules. That way
 core stop gracefully
works on the command-line interface (CLI): One module after the other is
unloaded. A recent change broke this for the module res_pjsip.

ASTERISK-27861

Change-Id: I261abcb411d026bbb0691cc78f28300bfd3103a3

res/res_pjsip_endpoint_identifier_ip.c

@@ -766,6 +766,7 @@ static int unload_module(void)
 	ast_cli_unregister_multiple(cli_identify, ARRAY_LEN(cli_identify));
 	ast_sip_unregister_cli_formatter(cli_formatter);
 	ast_sip_unregister_endpoint_formatter(&endpoint_identify_formatter);
+	ast_sip_unregister_endpoint_identifier(&header_identifier);
 	ast_sip_unregister_endpoint_identifier(&ip_identifier);
 
 	return 0;