main: set the identity in the logger

This causes "iwd" to be output in each message sent to syslog to help
quickly identify iwd messages.

src/main.c

@@ -531,6 +531,8 @@ int main(int argc, char *argv[])
 	else
 		l_log_set_stderr();
 
+	l_log_set_ident("iwd");
+
 	if (check_crypto() < 0)
 		return EXIT_FAILURE;