Use gofumpt to format code

gofumpt (mvdan.cc/gofumpt) is a fork of gofmt with stricter rules.

Brought to you by

	git ls-files \*.go | grep -v ^vendor/ | xargs gofumpt -s -w

Looking at the diff, all these changes make sense.

Also, replace gofmt with gofumpt in golangci.yml.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/network_linux.go

@@ -83,8 +83,7 @@ func readSysfsNetworkStats(ethInterface, statsFile string) (uint64, error) {
 }
 
 // loopback is a network strategy that provides a basic loopback device
-type loopback struct {
-}
+type loopback struct{}
 
 func (l *loopback) create(n *network, nspid int) error {
 	return nil