Allow stagers to bind to different ports than the resolved URL

[lorenzog]

Is your feature request related to a problem? Please describe.
Stager listeners appear to bind to the port supplied in the url parameter. It would be nice if one could specify a different port to bind a listener, to simplify the use of HTTP redirectors, allowing multiple stagers and re-using HTTP URLs.

Describe the solution you'd like
The stage-listener command could have a -p option, similar to how listeners are started, such as:

stage-listener --url https://stager.attackerdomain:443/blah -p 12345

This would create a job and start a listener on local port 12345. On the HTTP redirector server, which gathers traffic for 'stager.attackerdomain.com', one could then redirect traffic to /blah to port 12345 of the Sliver c2, and other URLs to the regular HTTP listener.

Describe alternatives you've considered
At the moment, starting a stage-listener forces me to use the same port on both the c2 server and the HTTP redirector.

Sliver is really good by the way, excellent work :)

[moloch--]

Already in the works for v1.6 :) no release date yet though.