multicast(4): Fix disabling multicast forwarding

[pouria]

Summary

multicast(4) mistakenly stated that multicast
forwarding can be disabled with MRT_INIT by setting
its value to 0.
Fix by adding MRT_DONE and MRT6_DONE.

Test Plan

mandoc -Tlint

[markj]

Thanks!

share/man/man4/multicast.4

149

I'd suggest a slightly different wording: When applied to the multicast routing socket, the .Dv MRT_DONE and .Dv MRT6_DONE socket options disable multicast forwarding in the kernel:

158

Closing the socket has the same effect, we could mention that here too.

[ziaee]

Agree with markj. Nit: commit message should be "multicast.4: Fix disabling multicast forwarding". "multicast(4)" could refer to changing the logic of the driver, but "multicast.4" clearly refers only to the manual page.

[bms]

Been spring-cleaning my cluster home directory, as I only regained access for the first time in nearly 10 years this morning UK time. This commit probably has some relevant history lessons.

[pouria]

@markj done. I reused your wording for closing the socket, does that work?
@ziaee done.
Thank you

[pouria]

@glebius Can I commit this?

[ziaee]

@bms This is very good info, thank you.