#copy this dir ASP/netns to /opt/ as root 
cp netns /opt/
chown -R root:root /opt/netns

# add with sudo visudo
user      ALL=(ALL) NOPASSWD:/opt/netns/_exec, /opt/netns/create

# now "user" can create "ip netns" with
sudo /opt/netns/create 14

# and attache as "user" any cmd to it with
/opt/netns/exec --id=14 --cmd=bash