slave channel doesn't listen on the proxy side

[vatral]

While the slave channel implementation can be used in any direction, due to a bug in the current code it fails to listen on the port on the nxproxy side.

Example with the original code:

/home/vadim/git/nx-libs/nxproxy/nxproxy -S localhost:100 slave=63330 media=40001 cups=40002
....
Info: Connection with remote proxy completed.
Info: No proxy cookie was provided for authentication.
Info: Forwarding the real X authorization cookie.
Info: Using LAN link parameters 1536/24/1/0.
Info: Using pack method 'adaptive-9' with session ''.
Info: Not using NX delta compression.
Info: Not using ZLIB data compression.
Info: Not using ZLIB stream compression.
Info: Not using a persistent cache.
Info: Forwarding X11 connections to display ':1'.
Info: Forwarding CUPS connections to port 'tcp:localhost:40002'.
Info: Forwarding auxiliary X11 connections to display ':1'.
Info: Forwarding multimedia connections to port 'tcp:localhost:40001'.
Session: Session started at 'Fri Feb 14 12:24:15 2020'.
Info: Established X server connection.
Info: Using shared memory parameters 0/0K.


$ netstat -apnlt | grep nxproxy
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        0      0 127.0.0.1:40214         127.0.0.1:4100          ESTABLISHED 716366/lt-nxproxy   
$