Add following lines in sysctl to increase kernel buffers as well : (default is 128k, following config will increase it to 16m)
vim /etc/sysctl.conf
net.core.rmem_default=16777216
net.core.wmem_default=16777216
net.core.rmem_max=16777216
net.core.wmem_max=16777216
sysctl -p to run it && restart nlbwmon.