Enable gofumpt extra rules

Commit b2f8a74d "clothed" the naked return as inflicted by gofumpt
v0.9.0. Since gofumpt v0.9.2 this rule was moved to "extra" category,
not enabled by default. The only other "extra" rule is to group adjacent
parameters with the same type, which also makes sense.

Enable gofumpt "extra" rules, and reformat the code accordingly.

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

libcontainer/utils/cmsg.go

@@ -114,7 +114,7 @@ func RecvFile(socket *os.File) (_ *os.File, Err error) {
 // SendFile sends a file over the given AF_UNIX socket. file.Name() is also
 // included so that if the other end uses RecvFile, the file will have the same
 // name information.
-func SendFile(socket *os.File, file *os.File) error {
+func SendFile(socket, file *os.File) error {
 	name := file.Name()
 	if len(name) >= MaxNameLen {
 		return fmt.Errorf("sendfd: filename too long: %s", name)