Ethernet bug at Upstream-v3.15-rcx on Lager.

[カオ ミン ヒェップ <cm-hiep@jinso.co.jp>]

Hi Sergei

I am Hiep from JINZAI SOLUTION (a Japanese Company).
Now, I am testing a upstream-v3.15-rc2 on Lager for Renesas RSO.
I found a problem about Ethernet Driver so I would like to report to you.
The problem is losing data when sending data by UDP:

     - From Lager board to PC:
     BANDWIDTH from 10M to 70M are good,  but they suddenly  down 51.2 
Mbits/sec at 80M
     and 57.8 Mbits/sec at 90 M and 64.2 Mbits/sec at 100M.

     - From PC to Lager board:
    Some time when the message of "sh-eth r8a7790-ether eth0: Receive 
FIFO Overflow" occurs,
    some of datagrams will be lost as the logs show below:
     「$ iperf -c 172.16.1.36 -u -b 90M
     .....
     [  3] Server Report:
     [  3]  0.0-10.0 sec   108 MBytes  90.4 Mbits/sec   0.000 ms 
36/76923 (0.047%)
     .....
     # iperf -s -u
     [ ID] Interval       Transfer     Bandwidth        Jitter 
Lost/Total Datagrams
     sh-eth r8a7790-ether eth0: Receive FIFO Overflow
     [  3]  0.0-10.0 sec   108 MBytes  90.4 Mbits/sec   0.001 ms 
36/76923 (0.047%)

Please review it when you have time.

Bests Regards,
Cao Minh Hiep.