add UDP socket counts and rename to 'netstat'.

Closes #244

plugins/system/NETSTAT_README.md

@@ -0,0 +1,52 @@
+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
+