[mail_notifier] Router hostname in message subject

This adds router host name into the subject of e-mail notification,
which is useful if someone has more than one Turris router.

mail_notifier/notifier

@@ -122,6 +122,12 @@ compose_message() {
 	local rand=`tr -dc A-Za-z0-9 < /dev/urandom 2>/dev/null | head -c8`
 	local domain=`uci get user_notify.smtp.from | cut -d '@' -f2`
 	local msg_id="<$date_time.$rand@$domain>"
+	local hostname=`cat /proc/sys/kernel/hostname`
+	if [ "$lang" = "cs" ]; then
+		local mail_subject="=?utf-8?Q?Upozorn=C4=9Bn=C3=AD?= od =?utf-8?Q?Va=C5=A1eho?= routeru $hostname"
+	else
+		local mail_subject="Notification from your router $hostname"
+	fi
 
 	local msg_list=`ls "$base_folder"`
 	for msg in $msg_list; do
@@ -201,7 +207,7 @@ compose_message() {
 		echo "Content-Type: text/plain; charset=UTF-8" >> "$msg_file"
 		echo "Date: $curr_date" >> "$msg_file"
 		echo "Message-ID: $msg_id" >> "$msg_file"
-		echo -e "Subject: =?utf-8?Q?Upozorn=C4=9Bn=C3=AD?= od =?utf-8?Q?Va=C5=A1eho?= routeru Turris\n" >> "$msg_file"
+		echo -e "Subject: $mail_subject\n" >> "$msg_file"
 		cat $msg_file.tmp >> "$msg_file"
 	fi