Variable for network device names

[kng]

Issue:
Too many virtual devices in the network graph.
When running vm's or docker etc, there can be quite a few interfaces cluttering the graphs.

Solution:
In the query for network stats, add the variable netdevices to select what interfaces you want to see,
containing something like: eth[0-9]+|enp[0-9]+s[0-9]+|eno[0-9]+
Probably a few more patterns.

Example query:
irate(node_network_receive_bytes_total{instance="$node",job="$job",device=~"$netdevices"}[$__rate_interval])*8