Update validation_whats-edns0-all-about.xml

Resolved some technical inaccuracies.
UDP packets can be larger than 512 bytes, and EDNS does not allow DNS data to be sent in "multiple packets over UDP".
The previous wording implied that the maximum size for UDP packets in general is 4096 bytes (is really 65535 bytes).
"the network gears" - pluralizing it makes it sound like a mechanical thing rather than referring to routers, switches, firewalls, etc
Even though I eliminated it, I'm not really opposed to the term "network gear", but it is more slangy or jargony than "network equipment"