Unclear error message when AP fails due to the WiFi adapter being in use

[erikarvstedt]

Describe the bug
When using linux-wifi-hotspot on a WiFi adapter that's already used as a client (like with wpa_supplicant), the linux-wifi-hotspot script hangs.

To Reproduce

1. Use wpa_supplicant to connect to a wireless network with adapter wlan0.
2. Create a WiFi hotspot on wlan0:

   create_ap wlan0 my-wan-iface myhotspot mypasswd

   Stdout:

   ...
   Sharing Internet using method: nat
   hostapd command-line interface: hostapd_cli -p /tmp/create_ap.wlan0.conf.28LbRTnt/hostapd_ctrl
   ap0: interface state UNINITIALIZED->ENABLED
   ap0: AP-ENABLED 
   ap0: INTERFACE-DISABLED 
   

   At this point, the script hangs.

Expected behavior
An error message that points to the cause of the error instead of the unspecific msg ap0: INTERFACE-DISABLED.

Environment
linux-wifi-hotspot 4.6.0
Adapter: Intel Corporation Wi-Fi 6 AX200 (kernel module iwlwifi)