Add fallback to resolveSystemAddr() in linux

[aboch]

• This PR is to address an issue with the swarm init address autodiscovery when the docker daemon is running inside a container.
  The issue (which was introduced by Only consider netlink "device" interfaces in address autodetection on Linux #25279) is that docker will always prompt the user to pass the advertise-addr option even when it should not be needed (only one ethernet interface present).
• The problem happens because in a container the ethernet interfaces are in fact veth interfaces, therefore the current logic would skip them, given it only looks for device type interfaces.
• The fix to cover this corner case is to have the linux auto-address logic fall back to the common auto-address logic being used in the other platforms, when no device type interface is found. The common autoaddress logic filtering relies on checking whether the prospect interface's address is not part of the subnets docker manages.

Signed-off-by: Alessandro Boch aboch@docker.com

[aboch]

ping @aaronlehmann

[aaronlehmann]

Tested and it works for me.

LGTM

[tonistiigi]

LGTM