Remove usage of pkg sockets and tlsconfig.

- Use the ones provided by docker/go-connections, they are a drop in replacement.
- Remove pkg/sockets from docker.
- Keep pkg/tlsconfig because libnetwork still needs it and there is a
  circular dependency issue.

Signed-off-by: David Calavera <david.calavera@gmail.com>

docs/registry.go

@@ -23,8 +23,8 @@ import (
 	"github.com/docker/distribution/registry/client/transport"
 	"github.com/docker/docker/dockerversion"
 	"github.com/docker/docker/pkg/parsers/kernel"
-	"github.com/docker/docker/pkg/tlsconfig"
 	"github.com/docker/docker/pkg/useragent"
+	"github.com/docker/go-connections/tlsconfig"
 )
 
 var (