Support for numeric 396

[henk84]

WARN -- rfc2812.rb:1393:in `process': Unknown message ":irc-02.netwichtig.ch 396 marvin 6CCEA49:322BA2D8:DD9B22A:IP :is now your displayed host"

Please support this message/numeric:
https://defs.ircdocs.horse/defs/numerics.html#rpl-visiblehost-396

It’s also mentioned in passing in https://ircv3.net/specs/extensions/multiline:

Clients might wish to perform a WHO query on themselves when connecting to a server, and keep track of numeric 396 RPL_VISIBLEHOST to keep their user@host mask in sync.