Retrieve rx/tx power data from EEPROM in openolt

the rx/tx power needs to be retrieved from openolt-agent.

A sample program is provided in the attachment.
We offer the example program for getting the EEPROM data. You could follow the steps to build the test tool.

1. In ONL build environment to compiler C++ source code.
g++ -std=c++11 -o test read_rx_power_threshold.cpp

2. scp test to GPON device.
scp <user_name>@<ip address>:<file_name> .

3. chmod 777 test
4. Plug in GPON transceiver into PON port 1
5. use the test tool
root@localhost:~# ./test
Rx_Power_Hi_Alarm[0.794300] mW [ -1.000]dBm
Rx_Power_Hi_Warning[0.631000] mW [ -2.000]dBm
Rx_Power_Low_Warning[0.006300] mW [ -22.007]dBm
Rx_Power_ow_Alarm[0.005000] mW [ -23.010]dBm