Fix nc commands while setting up the benchmark environment

Since a recent builders the nc command used in the benchmark pipeline is not working anymore.

This is due to a change in the CentOS/RockyLinux RPM repositories where NMap Netcat, a replacement of traditional nc command, has moved to the Base repository and former nc version is no longer available in EPEL repository.

It seems that the NMap nc command doesn't have the -N option, instead it has --send-only which seems to do the same thing.