fix BACKUP_FILE unbound variable and add ping to dep checks

setup-network.sh

@@ -26,7 +26,7 @@ check_deps() {
 
 [ "$(id -u)" -eq 0 ] || die "Run as root"
 
-check_deps ip netplan systemctl
+check_deps ip netplan systemctl ping
 
 header "TinyBoard Network Setup"
 
@@ -118,6 +118,7 @@ if $IS_WIFI; then
 fi
 
 header "Writing Netplan Config"
+BACKUP_FILE=""
 if [ -f "$NETPLAN_FILE" ]; then
     BACKUP_FILE="/root/$(basename "${NETPLAN_FILE}").bak"
     cp "$NETPLAN_FILE" "$BACKUP_FILE"