little changes in main script

usr/bin/t3hs/t3hs_sim800

@@ -122,11 +122,6 @@ EOF
 	local password="$5"
 	local iface="${6:-ppp0}"
 
-	if ip link show $iface > /dev/null 2>&1; then
-		echo "Interface $iface already exists"
-		exit 1
-	fi
-
 	args=""
 	if [[ -z $topic ]]; then
 		echo "topic must be provided to \`mqtt_off\` function"
@@ -209,5 +204,6 @@ case $# in
 	;;
 *)
 	print_usage
+	exit 1
 	;;
 esac