modem: uart interface does not disable TX interrupt in ISR

[JordanYates]

Describe the bug

The UART ISR handler modem_iface_uart_isr in modem_iface_uart.c does not disable the TX interrupt when executed.
For the uart_nrfx_uarte serial driver at least, this results in the UARTE ISR permanently triggering after the end of the first transmission.
This locks up the system.

To Reproduce

Place an esp-at device on a UARTE port and attempt to run the samples/net/wifi sample.

&uart0 {
	compatible = "nordic,nrf-uarte";
	current-speed = <115200>;
	status = "okay";
	tx-pin = <34>;
	rx-pin = <33>;
	rts-pin = <40>;
	cts-pin = <7>;

	esp32e16 {
		compatible = "espressif,esp-at";
		label = "esp32e16";
		status = "okay";
	};
};

By default, the application will not reach the boot banner.
Adding the following lines to the bottom of modem_iface_uart_isr resolves this issue:

	/* Disable the TX interrupt once tranmission is complete */
	if (uart_irq_tx_complete(ctx->iface.dev)) {
		uart_irq_tx_disable(ctx->iface.dev);
	}

Expected behavior
The interrupt should not be permanently triggered.

Impact
Applications fail to boot.

Environment (please complete the following information):

• Zephyr v2.7.0

[carlescufi]

@rerickson1 could you please take a look and send a PR if appropriate?

[rerickson1]

@rerickson1 could you please take a look and send a PR if appropriate?

I could submit a PR but have no way of testing this. @JordanYates could you submit a PR with your requested change?

[JordanYates]

I could submit a PR but have no way of testing this. @JordanYates could you submit a PR with your requested change?

Done

[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.