Fix port override in connect().

[stephen-mw]

At the moment, supplying a port to the connect() function is a no-op. It will always be replaced with the default port 5222 because pick_dns_answer always returns a default port.

It looks to me like the logic is reversed. If a port was explicitly supplied to connect then it should always be used. If not, fall back to whatever you get from the pick_dns_answer.

Feel free to close this an implement in another way if that's what you prefer.

How to repro:

xmpp = slixmpp.ClientXMPP(username, password)
xmpp.connect(address=("example.com", 9999))
xmpp.process()

DEBUG    Using selector: KqueueSelector
DEBUG    Loaded Plugin: RFC 6120: Stream Feature: STARTTLS
DEBUG    Loaded Plugin: RFC 6120: Stream Feature: Resource Binding
DEBUG    Loaded Plugin: RFC 3920: Stream Feature: Start Session
DEBUG    Loaded Plugin: RFC 6121: Stream Feature: Roster Versioning
DEBUG    Loaded Plugin: RFC 6121: Stream Feature: Subscription Pre-Approval
DEBUG    Loaded Plugin: RFC 6120: Stream Feature: SASL
DEBUG    Event triggered: connecting
DEBUG    DNS: Querying example.com for AAAA records.
DEBUG    DNS: Querying example.com for A records.
DEBUG    Connection failed: [Errno 61] Connect call failed ('2606:2800:220:1:248:1893:25c8:1946', 5222, 0, 0)
DEBUG    Event triggered: connection_failed

Note that the port fell back to the default 5222:

DEBUG    Connection failed: [Errno 61] Connect call failed ('2606:2800:220:1:248:1893:25c8:1946', 5222, 0, 0)

[xaimepardal]

I am waiting for this merge