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)
Fix derp patch application adding 'nil,' back to return in GOARCH check

Docker-DCO-1.1-Signed-off-by: Jason Plum <jplum@devonit.com> (github: WarheadsSE)
nudge broken aufs +build constraints

Docker-DCO-1.1-Signed-off-by: Jason Plum <jplum@devonit.com> (github: WarheadsSE)
Use the arm-linux-gnueabi to build for ARM - make cross now generates a valid arm binary

Docker-DCO-1.1-Signed-off-by: Praneeth <lifeeth@resin.io> (github: lifeeth)