Support IPv6 in snapserver

[miek]

This commit allows snapserver to listen on IPv4 and/or IPv6 when available, to go along with #273.

I've followed the example given in a boostcon presentation on IPv6 best practices here: https://raw.githubusercontent.com/boostcon/2011_presentations/master/wed/IPv6.pdf and so it should support systems with dual stack, IPv4 only or IPv6 only.

This works well for me and accepts clients on both IPv4 & IPV6:

$ ./snapserver 
Settings file: /home/mike/.config/snapserver/server.json
2017-09-26 16-00-50 [out] Adding service 'Snapcast'
2017-09-26 16-00-50 [out] PcmStream sampleFormat: 48000:16:2
2017-09-26 16-00-50 [out] PipeStream mode: create
2017-09-26 16-00-50 [out] Stream: {"fragment":"","host":"","path":"/tmp/snapfifo","query":{"buffer_ms":"20","codec":"flac","name":"default","sampleformat":"48000:16:2"},"raw":"pipe:///tmp/snapfifo?name=default","scheme":"pipe"}
2017-09-26 16-00-50 [err] (PipeStream) Exception: end of file
2017-09-26 16-00-51 [out] Service 'Snapcast' successfully established.
2017-09-26 16-00-54 [Notice] ControlServer::NewConnection: 2a04:5d00:70:64f1:bdf0:8419:e02b:4ef5
2017-09-26 16-01-25 [Err] Exception in ControlSession::reader(): read_until: End of file
2017-09-26 16-01-25 [Notice] ControlServer::NewConnection: ::ffff:10.64.10.107

I tried disabling IPv6 with

sudo sh -c 'echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6' 

and snapserver still comes up and works correctly on IPv4.

Also it would be easy to add a command-line option to set the bind address now, if you want that?

[badaix]

Really nice!

Client with IPv6: ./snapclient -h fe80::be5f:f4ff:feca:cd64%wlan0
Server:

2017-09-26 19-45-42 [Notice] StreamServer::NewConnection: fe80::221:6aff:fe7d:74fc%eth0
2017-09-26 19-45-43 [Info] Hello from d26b04e8811a544a693ac1e3540dd21d, host: T400, v0.11.1, ClientName: Snapclient, OS: Linux Mint 17.3 Rosa, Arch: x86_64, Protocol version: 2

Client with IPv4: ./snapclient -h 192.168.0.2
Server:

2017-09-26 19-46-02 [Notice] StreamServer::NewConnection: ::ffff:192.168.0.54
2017-09-26 19-46-02 [Info] Hello from d26b04e8811a544a693ac1e3540dd21d, host: T400, v0.11.1, ClientName: Snapclient, OS: Linux Mint 17.3 Rosa, Arch: x86_64, Protocol version: 2

[badaix]

manually merged into develop branch
Edit: Somehow GitHub didn't recognize the manual merge and didn't mention you as a contributor.
Any idea?

[miek]

Merge looks good to me, I think GitHub only counts contributions once it's in the master branch.

Cheers!

[badaix]

I did a reset of the first merge and hard pushed the result (bad practice in public repos). Hope no one pulled the latest changes from the develop branch during the last 10min.
Now I managed to merge the PR into develop using the GitHub GUI and it's now properly marked as merged, but still your not listed as contributor. I hope this will change when I merge the develop branch back into master.
Thanks again!

Edit: seems you're right. Looks like it counts just master contributions. According to GitHub I didn't contribute for the last few month, which is true for master, but not for develop