Add fallback interface for DNS listening behavior in case PIHOLE_INTERFACE is not set in setupVars.conf

Signed-off-by: DL6ER <dl6er@dl6er.de>

advanced/Scripts/webpage.sh

@@ -175,7 +175,13 @@ trust-anchor=.,20326,8,2,E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC68345710423
 		add_dnsmasq_setting "local-service"
 	else
 		# Listen only on one interface
-		add_dnsmasq_setting "interface" "${PIHOLE_INTERFACE}"
+		interface=$(grep 'PIHOLE_INTERFACE=' /etc/pihole/setupVars.conf | sed "s/.*=//")
+		# Use eth0 as fallback interface if interface is missing in setupVars.conf
+		if [ -z "${interface}" ]; then
+			interface="eth0"
+		fi
+
+		add_dnsmasq_setting "interface" "${interface}"
 	fi
 
 }