Bring the description of the sysctl(8) variable

net.graph.nonstandard_pppoe into accord with the reality.

MFC after:	1 week

share/man/man4/ng_pppoe.4

@@ -182,22 +182,26 @@ This node shuts down upon receipt of a
 control message, when all session have been disconnected or when the
 .Dv ethernet
 hook is disconnected.
-.Sh SYSCTLs
-If you are one of the unfortunate people who have an ISP that
-uses some "PPPoE" equipment from (I believe) 3com, and who have to
-use a different ethertype on PPPoE packets
-(hey why not change it from the standard for
-no reason?) then after you have kldloaded or compiled in your PPPoE node,
-you may have to do the following sysctl:
-.Bd -literal
-(kldload netgraph)
-(kldload ng_pppoe)
-sysctl net.graph.nonstandard_pppoe=1
-.Ed
-.Pp
-to enable the alternate ethertypes.
-Then phone your ISP and ask them
-why you need to set that option for you to be able to connect.
+.Sh SYSCTL VARIABLES
+The variable
+.Va net.graph.nonstandard_pppoe
+controls certain aspects of
+.Nm
+operation.
+Its default value of \-1 corresponds to standard mode
+and should suit nearly all purposes.
+A value of 1 will turn on compatibility with some particularly
+broken PPPoE implementations using nonstandard "ethertypes"
+in PPPoE packets.
+When in this mode, your PPPoE node will be unable to communicate
+with standard nodes.
+A value of 0 is deprecated.
+It was intended to turn on autodetection of the proper mode.
+.Bf -emphasis
+It will make your entire PPPoE network vulnerable
+to a denial-of-service attack,
+therefore its use is strongly discouraged.
+.Ef
 .Sh EXAMPLES
 The following code uses
 .Dv libnetgraph