Improve IP check

- Install iproute (for the "ip" command) in the unlikely cases that
  it is not already installed.
- Abort and exit if server IP cannot be detected.
- Cleanup

wireguard-install.sh

@@ -202,7 +202,7 @@ EOF
 show_header() {
 cat <<'EOF'
 
-WireGuard Script  3 Oct 2022
+WireGuard Script
 https://github.com/hwdsl2/wireguard-install
 EOF
 }
@@ -338,6 +338,25 @@ if [[ ! -e /etc/wireguard/wg0.conf ]]; then
 			apt-get -yqq install wget >/dev/null
 		) || exit 1
 	fi
+	if ! hash ip 2>/dev/null; then
+		if [ "$auto" = 0 ]; then
+			echo "iproute is required to use this installer."
+			read -n1 -r -p "Press any key to install iproute and continue..."
+		fi
+		if [ "$os" = "debian" ] || [ "$os" = "ubuntu" ]; then
+			export DEBIAN_FRONTEND=noninteractive
+			(
+				set -x
+				apt-get -yqq update || apt-get -yqq update
+				apt-get -yqq install iproute2 >/dev/null
+			) || exit 1
+		else
+			(
+				set -x
+				yum -y -q install iproute >/dev/null
+			) || exit 1
+		fi
+	fi
 	if [ "$auto" = 0 ]; then
 		echo
 		echo 'Welcome to this WireGuard server installer!'
@@ -387,6 +406,11 @@ if [[ ! -e /etc/wireguard/wg0.conf ]]; then
 			fi
 		fi
 	fi
+	if ! check_ip "$ip"; then
+		echo "Error: Could not detect this server's IP address." >&2
+		echo "Abort. No changes were made." >&2
+		exit 1
+	fi
 	# If $ip is a private IP address, the server must be behind NAT
 	if printf '%s' "$ip" | grep -qE '^(10|127|172\.(1[6-9]|2[0-9]|3[0-1])|192\.168|169\.254)\.'; then
 		find_public_ip