daemon: move sortMounts to a platform-agnostic file

The same code was used both on Linux and Windows; move it to a platform-
agnostic file so that both can use this function, which contains GoDoc
describing the functionality.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/volumes_unix.go

@@ -6,7 +6,6 @@ import (
 	"context"
 	"fmt"
 	"os"
-	"sort"
 	"strconv"
 	"strings"
 
@@ -121,14 +120,6 @@ func (daemon *Daemon) setupMounts(ctx context.Context, c *container.Container) (
 	return append(mounts, netMounts...), cleanups.Release(), nil
 }
 
-// sortMounts sorts an array of mounts in lexicographic order. This ensure that
-// when mounting, the mounts don't shadow other mounts. For example, if mounting
-// /etc and /etc/resolv.conf, /etc/resolv.conf must not be mounted first.
-func sortMounts(m []container.Mount) []container.Mount {
-	sort.Sort(mounts(m))
-	return m
-}
-
 // setBindModeIfNull is platform specific processing to ensure the
 // shared mode is set to 'z' if it is null. This is called in the case
 // of processing a named volume and not a typical bind.