dns-server: Fix netstat on Catalina

[mf2k (Frank Schima)]

See ​https://github.com/macports/macports-ports/pull/4713#issuecomment-507355700.

[essandess (Steve Smith)]

@mf2k @kencu @tobypeterson @raimue

Following up on the discussion at ​https://github.com/macports/macports-ports/pull/4713 here.

The 10.15 netstat issue is part of the larger issue of how to access network information on install.

Would you all please offer feedback on these Portfile design questions?

1. The entire reason for populating variables with local network information is to provide a basic working DNS server on the LAN. It is expected that user will have to modify the resulting files themselves anyway, but at least the initial install will work. But these network settings could just as well be hard-coded with a domain name like please-edit-the-named-db-configuration-yourself.com with IP address 192.168.0.2 or 10.0.1.2. Should this port use fixed variables for the example setup and do away with the network discovery shell stuff entirely?

2. If we keep the network settings and calls to netstat and the like, that will necessitate a macOS-version-specific block for these calls. What's the MacPorts Way of doing this?

3. I get that using the shell is undesirable if avoidable (but I object to "objectionable"!); however, I'm not aware of a way around it. And if we're already issuing a call to netstat, I don't see the benefit of string handling within tcl rather than just a few sed calls.

[jmroot (Joshua Root)]

The objectionable part is doing all that shelling out just to parse the portfile. It would be acceptable if it only happened when installing.

[essandess (Steve Smith)]

In e71ee76812fdb3680c25fd5d2f09f710486cecc1/macports-ports (master):

dns-server: Add hard-coded network settings to address portindex issue

• Use default hard-coded example configuration settings
• Put network settings in post-activate block as recommended
• Use awks's $NF to get default interfaces
• Resolves: #58668

[essandess (Steve Smith)]

In 9010c9428a0acabc6fe8f0ca7d68614376b5daae/macports-ports (master):

macos-vpn-server: Add hard-coded network settings to address portindex issue

• Use default hard-coded example configuration settings
• Put network settings in post-activate block as recommended
• Use awks's $NF to get default interfaces
• Related: ​https://github.com/macports/macports-ports/pull/4741
• Related: #58668