example.sh: remove useless mc_forwarding lines

[leoplo]

As far as I know, mc_forwarding is not a writable variable :

nexedi@red:~/multicast$ ls -ln /proc/sys/net/ipv6/conf/all/mc_forwarding
-r--r--r-- 1 0 0 0 Jan 27 11:10 /proc/sys/net/ipv6/conf/all/mc_forwarding

nexedi@red:~/multicast$ ls -ln /proc/sys/net/ipv4/conf/all/mc_forwarding
-r--r--r-- 1 0 0 0 Jan 27 11:10 /proc/sys/net/ipv4/conf/all/mc_forwarding

If it is not writable then its presence in the example is confusing.

To set this sysctl variable to True one needs to activate kernel's mroute code.

But maybe it does not always have been the case.

[Oryon]

Hello !
My best guess is that things have changed in 5+ years. This variable used to be writable and is not anymore.
Removing it without proposed alternative would be even more misleading though ?
Maybe have the script try to set it to one and, in case of failure, display a message saying mroute should be enabled ?

[leoplo]

Maybe have the script try to set it to one and, in case of failure, display a message saying mroute should be enabled ?

mrib_init enables mroute so no user's action is required.

Furthermore it does not really causes a failure (at least on Debian, I am not so sure it is also true on RedHat) :

user@debian:~$ sudo sysctl -w net.ipv6.conf.all.forwarding=1
net.ipv6.conf.all.forwarding = 1
user@debian:~$ sudo sysctl -w net.ipv6.conf.all.mc_forwarding=1
sysctl: setting key "net.ipv6.conf.all.mc_forwarding"

My best guess is that things have changed in 5+ years.
This is what I cannot figure. Until now I read about people facing mc_forwarding being read-only up to 2011.

If it does not cause any failure and there is a retro compatibility reason to have it then no change is required (maybe just commenting that this is useless for current kernel versions). However as I cannot find in which kernel version this was possible.