Increase PACKETS_PER_BUFFER to 65536

Increase PACKETS_PER_BUFFER to 65536

1) This mainly increase PACKETS_PER_BUFFER to 65536 to reduce the
frequency of TCP client acks.

2) Also kills TCP_BUFF_SIZE and define each buffer size in a
more intuitive way.

3) Free more unused memory to prevent being killed by oom-killer
after enlarged PACKETS_PER_BUFFER.

4) Increase client's select() timeout to 20 secs, since we encountered
timeout due to CPU busy in the same BM but with 20 VMs.

Tested this PS in a 10 VM node env, and it can multicast a 2.7G
file to 10 VMs in 6 minutes, while unicast needs 30+ minutes.

Change-Id: Iaf862fb1f1259cc770f720ccdd95dcc281aef262
Signed-off-by: Zhijiang Hu <hu.zhijiang@zte.com.cn>