[Outbound-Proxy] Use SRV Logic only if remote-port is not defined

[bundasmanu]

At this phase SRV logic is used if we don't pass a port in the SIP URI of Outbound-Proxy flag (-p flag). But, SRV lookup will be executed even if we pass a remote port before (-r flag). And for my perspective, SRV lookup should be skipped, if we pass a specific remote port in the command.
The change added is not abusive, and seems to not break anything. If we want to continue use SRV lookup, it's enough to didn't provide remote-port flag, of pass it after -p flag.

Tested with multiple transports, and passing IPs and hostnames. Also with port (in the -p flag), and with remote-port flag.

Thanks @nils-ohlmeier