install_netsniff-ng.sh: add provisioning script

Written for CentOS to install *most* (ifpps trafgen bpfc flowtop mausezahn) of the Netsniff-NG toolkit.
Edit to install curvetun (see comments in install_netsniff-ng() ).
Astraceroute and Netsniff-NG builds fail (lack of TPACKET_V3 on EL systems), so skip.