users by server port (eg 6667, 6697, 8000, etc).
This also adds security-group::exclude-server-port for consistency.
And in crules the function server_port() returns the server port number,
so you can use rule 'server_port()>6690' for example.
Note that for remote clients this will only work after previous
commit (b2d0ec1af3) is loaded on all
servers, otherwise all remote clients are seen as having a server_port
of zero (0). Though you probably usually only care about this on local
users anyway.
Bram Matthys
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