HBSD: use fetch_update for 'download only'

We now use the fetch_update for 'download only' function.
This function has the advantage to control the checksum of the download file.
Please note that there is no more resumption of the interrupted download.
Reported-by: Shawn Webb <shawn.webb@hardenedbsd.org>
Signed-off-by: Loic <loic.f@hardenedbsd.org>

usr.sbin/hbsd-update/hbsd-update

@@ -406,7 +406,12 @@ fetch_update() {
 		fi
 	fi
 
-	# Step 3: Untar the update archive
+	# Step 3: Check whether to continue
+	if [ ${downloadonly} = 1 ]; then
+		exit 0
+	fi
+
+	# Step 4: Untar the update archive
 	${TAR} -xf ${tmpdir}/update.tar \
 		-C ${tmpdir}
 	res=${?}
@@ -1258,9 +1263,8 @@ main() {
 	fi
 
 	if [ ${downloadonly} = 1 ]; then
-		debug_print "[*] Download the latest update to the current folder."
-		${FETCH} ${net_flag} -o update-$(get_version).tar -arR \
-		${baseurl}/update-$(get_version).tar
+		debug_print "[*] Download the latest update in ${tmpdir}"
+		fetch_update
 		exit 0
 	fi