Use a fixed list height for network interface selection

This solves the issue reported here: https://github.com/pi-hole/pi-hole/issues/4196
It replaces the other suggested solution here: https://github.com/pi-hole/pi-hole/pull/4197

The benefit of using a fixed/limited list height, compared to allowing larger whiptail/dialogue dimension, is that it works on small screens as well, where the screen or console size itself is too small to hold the interface list + text above + whiptail frame.

It the amount of list elements exceeds the defined list height, automatically a visual scroll bar is added and the list can be scrolled with up/down pageup/pagedown buttons, hence it is generally not required to adjust a list height based on the amount of elements. The fixed height of "6" is chosen since all other "--radiolist" calls use this fixed height as well, it fits and looks good within a 20 rows high whiptail dialogue, and in the common Pi-hole use cases there are no more than 6 network interfaces.

Signed-off-by: MichaIng <micha@dietpi.com>

automated install/basic-install.sh

@@ -674,7 +674,7 @@ chooseInterface() {
         # Feed the available interfaces into this while loop
         done <<< "${availableInterfaces}"
         # The whiptail command that will be run, stored in a variable
-        chooseInterfaceCmd=(whiptail --separate-output --radiolist "Choose An Interface (press space to toggle selection)" "${r}" "${c}" "${interfaceCount}")
+        chooseInterfaceCmd=(whiptail --separate-output --radiolist "Choose An Interface (press space to toggle selection)" "${r}" "${c}" 6)
         # Now run the command using the interfaces saved into the array
         chooseInterfaceOptions=$("${chooseInterfaceCmd[@]}" "${interfacesArray[@]}" 2>&1 >/dev/tty) || \
         # If the user chooses Cancel, exit