Fix server crash on request.server_port when bound to IPv6.

[Tronic]

If no X-Forwarded-Port nor Host headers are present, Sanic uses "sockname"
to determine the port. This expected (host, port) tuple to be returned but
for IPv6 a 4-tuple is returned instead. Changed code so that port is picked
up in either case. Handling of "peername" was already correct in this regard.

_get_address and server_port both still return incorrect data or crash for
other socket types (e.g unix). Socket type should checked before any queries.

[codecov]

Codecov Report

Merging #1640 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1640   +/-   ##
=======================================
  Coverage   91.61%   91.61%           
=======================================
  Files          19       19           
  Lines        2099     2099           
  Branches      391      391           
=======================================
  Hits         1923     1923           
  Misses        138      138           
  Partials       38       38

Impacted Files	Coverage Δ
sanic/request.py	97.58% <100%> (ø)	⬆️

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[Tronic]

import sanic
app = sanic.Sanic()
app.get("/")(lambda req: sanic.response.text(
    f"server_name={req.server_name}, server_port={req.server_port}\n"
))
app.run("localhost")

Provided that localhost resolves to ::1, run server and test by: curl [::1]:8000
Current git master: Internal Server Error
This pull request: server_name=[, server_port=8000
Pull request #1638: server_name=[::1], server_port=8000