Improve documentation for Serf WAN port

[sonnysideup]

After reading #3058 and the docs outlining the ports used by Consul, I now suspect that I should set both Serf LAN and WAN ports to 8302 but the docs did not provide me with obvious confirmation.

The documentation currently reads:

Serf WAN (Default 8302). This is used by servers to gossip over the WAN to other servers. TCP and UDP. As of Consul 0.8, it is recommended to enable connection between servers through port 8302 for both TCP and UDP on the LAN interface as well for the WAN Join Flooding feature. See also: Consul 0.8.0 CHANGELOG and GH-3058

Would it not be better to articulate this port like so:

Serf WAN (Default 8302). This is used by servers to gossip over the WAN to other servers. TCP and UDP. As of Consul 0.8, it is recommended that you configure the LAN and WAN interfaces to both use port 8302; the WAN Join Flooding feature leverages LAN membership. See also: Consul 0.8.0 CHANGELOG and GH-3058

This is a minor point but I decided I needed to create this issue after another developer and I agreed that the current wording is mildly confusing.

[pearkes]

Agree, we'd definitely appreciate a PR clarifying this!

[sonnysideup]

@pearkes Please let me know if you want to me to tweak the language here and/or make other changes.

[hanshasselberg]

Docs have been updated!