Enable nstat input plugin for softnet_stat data

Since we added to nstat's telegraf plugin the possibility
to collect data from `/proc/net/softnet_stat` regarding
dropped packets and rx_net_action a.k.a time squeeze, we need to enable
it globally on all hosts.

Also grafana dashboard update to include new graphs + added four
new Prometheus alers.

Related-Bug: PROD-21090

Change-Id: I9dfe87bdc8b677a51e3f305dd3c75c7d4cc4e0d4
4 files changed