Add new setting AllowConnFromSubnets

[ijc]

This is a fine grained version of AllowConnFromAll which allows configuration
of specific subnets or hosts.

Checklist

• contribution does not duplicate one of our existing pull requests
• contribution is in a branch rebased against master
• code compiles successfully without errors
• code follows the MythTV Coding Standards
• documentation added/updated/removed where necessary
• commits are logically organised and have good commit messages

[ijc]

I was unsure where to document this, I don't find the existing AllowConnFromAll anywhere in the wiki and the google hits are all the code & the original trac ticket https://code.mythtv.org/trac/ticket/13024 that added it.

[bennettpeter]

It is documented here in the wiki
https://www.mythtv.org/wiki/Setup_General#Host_Address_Backend_Setup_.28v29.29

[ijc]

@bennettpeter thanks, I failed to find it because it doesn't mention the db name, which now I think of it makes perfect sense since that's really an internal detail.

I'm just about to turn in for the night so I'll propose some words for the wiki here later.

[garybuhrmaster]

As I recall, QHostAddress::parseSubnet did not support IPv6 addresses. Has that been fixed in Qt?

[garybuhrmaster]

As I recall, QHostAddress::parseSubnet did not support IPv6 addresses. Has that been fixed in Qt?

Never mind, I found my own answer, it has been fixed for IPv6 (later than I would have liked, which should have happened over a decade ago).

[stuarta]

@ijc Can you raise an issue describing what the issue is that this is resolving please?

[ijc]

@stuarta done, please see #339.