ARM Linux platform support for docker

* Primarily +build constraint changes
* pkg/netlink: setBridgeMacAddress needed byte sign-edness handling.
* daemon/graphdb/btrfs: needed fsType constant representation handling.

Docker-DCO-1.1-Signed-off-by: Jason Plum <jplum@archlinuxarm.org> (github: WarheadsSE)

Replaces prior PR#5339