Telegraf plugin: NETSTAT

#### Description

The NETSTAT plugin collects TCP connections state and UDP socket counts by using `lsof`.

Supported TCP Connection states are follows. 

- established
- syn_sent
- syn_recv
- fin_wait1
- fin_wait2
- time_wait
- close
- close_wait
- last_ack
- listen
- closing
- none


# Measurements:
### TCP Connection State measurements:

Meta:
- units: counts

Measurement names:
- tcp_established
- tcp_syn_sent
- tcp_syn_recv
- tcp_fin_wait1
- tcp_fin_wait2
- tcp_time_wait
- tcp_close
- tcp_close_wait
- tcp_last_ack
- tcp_listen
- tcp_closing
- tcp_none

If there are no connection on the state, the metric is not counted.

### UDP socket counts measurements:

Meta:
- units: counts

Measurement names:
- udp_socket

