Fix missing generation of waiting-time-extension in some situations

In the function set_tpdu_state(), there is a missing transition to
WAIT_TX state. This is fine if you are coming from the WAIT_PB state,
which has already restarted the waiting timer via
card_emu_uart_update_wt(), but if you are coming from the WAIT_RX
state, then card_emu_uart_update_wt() is never called and the USART
timer is never restarted.  (Because the transmitter is left enabled in
WAIT_RX, the response is still sent to the modem; it is just the
half-wait timeouts that are missing).

Change-Id: Ib4eb964c073192e8f067004625af818ba2caf003

firmware/libcommon/source/card_emu.c

@@ -775,6 +775,15 @@ static void set_tpdu_state(struct card_handle *ch, enum tpdu_state new_ts)
 		/* prepare to extend the waiting time once half of it is reached */
 		card_emu_uart_update_wt(ch->uart_chan, ch->waiting_time);
 		break;
+	case TPDU_S_WAIT_TX:
+		/* If we came from WAIT_RX, disable the receiver and
+		 * enable the transmitter. If we came from WAIT_RX or
+		 * WAIT_PB, reset the waiting time so that we can extend
+		 * waiting time if needed. */
+		card_emu_uart_enable(ch->uart_chan, ENABLE_TX);
+		/* prepare to extend the waiting time once half of it is reached */
+		card_emu_uart_update_wt(ch->uart_chan, ch->waiting_time);
+		break;
 	default:
 		break;
 	}