Update telegraf to capture discard counters from `ethtool` for `mlx0`

roles/telegraf/templates/telegraf.conf.j2

@@ -119,6 +119,12 @@
   # Uncomment the following line if you do not need disk serial numbers.
   # skip_serial_number = true
 
+# Read ethtool for one interface only
+[[inputs.ethtool]]
+  interface_include = ["mlx0"]
+  fieldpass = ["rx_discards_phy", "tx_discards_phy"]
+  interval="60s"
+  
 # Collect statistics about itself
 [[inputs.internal]]
  ## If true, collect telegraf memory stats.