I was taking the wrong server address, I was taking the ip from eth0 instead of eth1. Once I changed that, check_nrpe start working also under xinetd and without -n flag.
/usr/local/nagios/libexec/check_nrpe -H 192.168.5.110
Also nagios plugins are working perfectly.
/usr/local/nagios/libexec/check_nrpe -H 192.168.5.110 -c check_total_procs
PROCS CRITICAL: 38 processes
Thanks a lot for your time and patience MensaWater.
I hope this post could help someone in the future.