freetdm: fix sip header wrong value of NADI

         error was caused by printing string value to integer

libs/freetdm/mod_freetdm/mod_freetdm.c

@@ -1710,7 +1710,7 @@ ftdm_status_t ftdm_channel_from_event(ftdm_sigmsg_t *sigmsg, switch_core_session
 		
 		var_value = ftdm_sigmsg_get_var(sigmsg, "ss7_clg_nadi");
 		if (!ftdm_strlen_zero(var_value)) {
-			switch_channel_set_variable_printf(channel, "sip_h_X-FreeTDM-NADI", "%d", var_value);
+			switch_channel_set_variable_printf(channel, "sip_h_X-FreeTDM-NADI", "%s", var_value);
 		}
 
 		var_value = ftdm_sigmsg_get_var(sigmsg, "ss7_rdnis_screen_ind");