Fix netns directory permissions

[disconnect3d]

Changed created netns directory permissions from 644 (-w----r--) to 0644 (rw-r--r--) when calling MkdirAll(...).

PoC:

dc@jhtc:~/gogo/makedir$ cat main.go
package main

import "os"

func main() {
    os.MkdirAll("644", 644)
    os.MkdirAll("0644", 0644)
}
dc@jhtc:~/gogo/makedir$ go run main.go
ls dc@jhtc:~/gogo/makedir$ ls -la
total 20
drwxrwxr-x 4 dc dc 4096 Jun  9 17:10 .
drwxrwxr-x 5 dc dc 4096 Jun  9 17:10 ..
drw-r--r-- 2 dc dc 4096 Jun  9 17:10 0644
d-w----r-- 2 dc dc 4096 Jun  9 17:10 644
-rw-rw-r-- 1 dc dc  101 Jun  9 17:05 main.go

Note: I found this issue via static analysis. I am not involved in this project and I don't have time to add tests etc.

PS: Can you accept this commit being not signed off? ;)