net/mwan3: update hint in mwan3.user for connected/disconnected

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/mwan3/files/etc/mwan3.user

@@ -7,6 +7,10 @@
 #
 # There are three main environment variables that are passed to this script.
 #
-# $ACTION	Either "ifup" or "ifdown"
+# $ACTION
+#      <ifup>         Is called by netifd and mwan3track
+#      <ifdown>       Is called by netifd and mwan3track
+#      <connected>    Is only called by mwan3track if tracking was successful
+#      <disconnected> Is only called by mwan3track if tracking has failed
 # $INTERFACE	Name of the interface which went up or down (e.g. "wan" or "wwan")
 # $DEVICE	Physical device name which interface went up or down (e.g. "eth0" or "wwan0")